Apple seeds first OS X 10.11.3 El Capitan beta to developers
Following today's iOS 9.2.1 beta release, Apple issued the first version of OS X 10.11.3 El Capitan to developers with minor improvements and bug fixes.

Aside from the usual stability, compatibility and security updates, the seed notes accompanying build 15D9c do not provide a detailed rundown of the exact changes included in today's OS X 10.11.3 beta release. A more detailed list, as well as focus areas for testing, should be included in the second beta release.
Apple's last update for the Mac operating system, OS X 10.11.2, dropped last week with a handful of improvements relating to Wi-Fi reliability, Handoff and AirDrop, Mail issues and iCloud Photo Sharing for Live Photos. The release also addressed a number of minor usability issues, bugs and security flaws.
The OS X 10.11.3 beta is the third seed to see release hit in as many months. Apple issued OS X 10.11.1 in late October, about one month after El Capitan debuted on Sept. 30.
Developers can download OS X 10.11.3 from the Mac App Store or Apple's developer portal.

Aside from the usual stability, compatibility and security updates, the seed notes accompanying build 15D9c do not provide a detailed rundown of the exact changes included in today's OS X 10.11.3 beta release. A more detailed list, as well as focus areas for testing, should be included in the second beta release.
Apple's last update for the Mac operating system, OS X 10.11.2, dropped last week with a handful of improvements relating to Wi-Fi reliability, Handoff and AirDrop, Mail issues and iCloud Photo Sharing for Live Photos. The release also addressed a number of minor usability issues, bugs and security flaws.
The OS X 10.11.3 beta is the third seed to see release hit in as many months. Apple issued OS X 10.11.1 in late October, about one month after El Capitan debuted on Sept. 30.
Developers can download OS X 10.11.3 from the Mac App Store or Apple's developer portal.
Comments
As always my first suggestion is get your hands on Disk Warrior v5 and see if you have damaged directories on the Mac. Disk Utilities is good but simply does not correct this problem. If you have another Mac you can run DW from that and mount the Mac mini using Target Mode. If not you'd need to boot to another disk as DW can only repair a dismounted drive. Believe me it is worth trying.
If you still have issues I'd back up and reinstall OS X from scratch and migrate the user folder back. If you still have issues it's something in you installed most likely.
Issue #1 - I have Alex read to me all the time. I'll highlight the text of an article and have him read to me while I'm busy doing something else. In el Capitan, Alex will skip words, or cut off words. It's typically at the beginning or end of a sentence. This never happened before, and is rather annoying. I've written to Apple about this issue, but one never knows if those mails ever really get read. Alex also has a problem reading bullet points. If there is an article with a couple bullet points and there's more than one line of text to a bullet, Alex says "bullet, bullet" at the beginning of every line of text.
Issue #2 - Slideshow playback is an issue when there are panoramic photos involved. The screen will noticeably drop frames and stutter. While I know that Apple in their infinite wisdom decided to put a 2012 gpu in a 15,1, one would expect it to be able to handle panning across panoramic photos in a slideshow without so much as a hiccup. I deleted everything in Photos and started from scratch, and it persists. The same problem occurs when viewing an exported slideshow (at 1080p) in full screen. One would think that the GPU could overclock when it needed to, but it doesn't seem to be doing the job when it comes to panoramic shots (all shot with an iPhone 6 Plus).
Issue #3 - The bubble of text that pops up when you put your cursor over an App in the Dock will remain after the App is launched. Sometimes the Dock will remain magnified after the App is launched. Moving the cursor over the App again corrects it. It's more of an annoyance than anything. It just serves as a reminder that I'm not satisfied with el Capitan as it currently exists.
As I stated previously, I've written to Apple about this using their feedback page https://www.apple.com/feedback/macosx.html and I would hope these issues would be addressed. I know that just because it's happening to me, doesn't mean it's happening to everyone. I've been with Apple since System 7. I'm just writing this here because I'm frustrated with these issues and never feel that Apple is actually listening.