M4 Mac mini may have a USB-C connectivity problem
Some M4 Mac mini owners are discovering USB-C issues with their new desktops, with peripherals disconnecting seemingly at random.

M4 Mac mini
USB is a fairly resilient technology, with the expectation that things connected using it will typically remain functional for a very long time, outside of external effects. However, it seems that in a small number of cases, USB-C connections on the M4 Mac mini are problematic.
Various Internet posts uncovered by AppleInsider reveal that users are undergoing similar problems. They generally consist of hardware connected using USB-C suddenly disconnecting and becoming unusable, or not connecting in the first place.
Going down
The reports uncovered in its investigation cover a range of time, ever since the M4 Mac mini's release in late 2024.
In one Reddit example posted on January 15, a poster explains that their USB-C keyboard "intermittently disconnects" and requires a physical disconnect and reconnect to start working again. To rule out other hardware issues, the same keyboard was working fine on the user's other Macs, with the issue only manifesting on the M4 Mac mini.
Other respondents complained that they had similar issues when using docks connecting with USB 3, as well as a KVM switch failing to work after waking the Mac mini. After a physical disconnection and plugging it back in, everything worked fine.
Another said it was only an issue with the rear ports, as the freezes didn't manifest when using the front ports.
A post from the end of December also asked if users had power issues with USB-C devices working off the M4 Mac mini. An external hard drive attached via USB-C disconnected when an "I/O heavy" task was performed, even when directly connected.
Others raised their problems again, with hubs not working with the ports but still working elsewhere. Questions were raised over the power draw of connected devices, as well as whether it was a front or rear USB problem, though it seems not to be limited to the rear set.

There are front ports on the new M4 Mac mini
An earlier post from November also brought up a failure in hub connectivity. However, in that instance, the poster said they were using an external power source for the hub instead of relying on bus power.
One respondent in that instance said that their USB-C devices didn't reconnect automatically on their M4 Mac mini, unlike their M1 Mac mini. Again, they had to physically reconnect the devices for them to work.
The issue has also appeared on the Apple Support Forum. One November 23 post explained that the front USB-C ports worked fine, but the rear ports wouldn't work reliably with connected devices, effectively making the rear ports useless.
Replies also included others who had similar problems, with hard drives connecting to USB-C at the front working, but not mounting to the rear.
These signal dropouts can be annoying to users and can be down to a number of reasons.
Elsewhere, the same problem appeared on the MacResource forum, with a user reporting a similar issue. They discovered that the Apple Extended Keyboard didn't work around the back when plugged in via an adapter, but a Logitech mouse plugged in directly worked.
The front ports apparently worked fine in that case.
Puzzling problem
The issue is a difficult one to diagnose, due to the sheer number of variables at play. Since users have complained that it happens when their hardware sleeps, this may also be something that Apple could issue a software update to fix.
Away from Apple, most users may find that they can do a number of checks to make sure it's not a problem they inadvertently caused. Inspecting the cable for damage, including looking for debris in the ports, will help, as well as trying a known-good cable in the setup.
The use of cheap USB-A to USB-C adapters and hubs may also be causing issues, as can poorly constructed cables. Checking these and replacing them if warranted could help the situation for the average user.
There should also be some thought about what devices are connected to which port on a Mac in general. It's not a good idea to have multiple bus-powered devices drawing power from the same single USB-C port on a host Mac.
Something like this could be solved with a powered hub or dock.
Read on AppleInsider

Comments
Overnight, Migration Assistant successfully moved everything via WiFi from my M2 Pro Mac mini (32GB Ram, 10GB Ethernet and 2TB SSD) to the new unit.
Both units had their own Magic Keyboard and my Logitech mouse has 3 switchable Bluetooth connections so it worked with both devices. Had to constantly switch the Apple monitor cable for the Studio Display between the two units to get Migration Assistant going. I had the keyboard connected with a Lightning to USB-C cable to one of the M4 Pro front USB-C slots.
Once done, I added the USB-C cable to the Raid drive to the new mini on the back along with the Studio Display cable. The Logitech mouse and new Magic Keyboard connect vis Bluetooth. I had issues with the Studio Display because I used the prior LG monitor's cable. Putting the Apple Display cable that came with it cured the waking up of the screen issue.
So far so good. Also SMP and VNC connections over 10Gb ethernet worked where they did not on the prior unit. Both units were on MacOS 15.2 operating system.
Wondering if the issue with the earlier M4 mini models could be operating system issues if not on latest release? Or, perhaps the issue did not happen with the M4 Pro chip models?
I have had a very stable USB environment using an OWC Thunderbolt 4 Dock (11 port) since 2021. Then right after the latest MacOS 15 upgrade several of my UISB devices lost connectivity. After offloading my USB-A devices to an OWC Thunderbolt 3 mini Dock most came back up but the CyberPower UPS USB-A continues to lose connectivity intermittently.
So it looks like this is on Apple's software.
If there were a non-ground electrical connection inside your Mac touching the case of your Mac the power supply’s short circuit protection would cause the Mac to crash.
USB issues can be very difficult to diagnose at the system level. The best way to troubleshoot USB issues would be to use a hardware USB protocol analyzer/ sniffer.
USB is a general purpose serial bus using a host controller (master) that orchestrates all of the communication between up to 127 nodes on each bus, including the controller itself, attached devices and hubs (slaves). Multiple USB busses can be connected together in a tiered topology, with each bus having it’s own controller. USB is not deterministic because communication is scheduled by the master, all devices on a bus share the available bandwidth, and messages are packetized so they must be marshaled and un-marshaled (reassembled) on both ends. However, USB has improved its bandwidth to such a degree since its inception that it can still be used in applications that need very high speed data transfers, e.g., streaming and isochronous control. You could say that in a fixed topology setup USB can be considered to provide bounded determinism, but not absolute determinism. It’s simply doing so much more than GPIB so there are more opportunities for errors.
"The device is no use to me as it continually loses peripherals which means multiple times a day I'm juggling port connections. Additionally, several times it's lost both keyboard and mouse and I have to re-start, which is very annoying if I have a number of accounts logged in with different work open."
Front and back ports, cables verified as good.
But my M1 Ultra Mac Studio has suddenly started (after all this time since new with no changes to any
cables) having resets at night. A new Gremlin to chase down.