A beta is by definition software that you shouldn't consider stable. When Google has trouble keeping bugs at bay even in its release software, we don't expect much from betas. But Android Q beta 3 is proving to be a little problematic — possibly even more so than Beta 2. The new gesture navigation is half-baked and breaking things left and right, snoozing for notifications has disappeared, and there's a bug that could cause you to disable your SIM card without intending to. All of these issues weren't there in Beta 2, and still we're discovering more problems as we go.
The latest to pop up concerns the Battery optimization menu (under Settings > Apps & notifications > Special app access). The menu is simply crashing every time we try to open it, be it on an Asus Zenfone 5Z or a Pixel 3 XL. With it inaccessible, it's impossible to turn on/off optimization for certain apps, so you're stuck with whatever you had chosen prior to upgrading to Beta 2.
If you want an app to be functional all the time even in the background (say your security camera app, smart door lock app, or other apps that require always-on location to keep their status updated), you won't be able to disable optimizations if you install it after you update to Beta 3. So you'll be stuck with Doze killing that background process all the time. Good going, Google.