[Xperia Z4 Tablet Q&A, Help & Troubleshooting] jelbo:
Well, some people have Xposed running just fine. I suspect they have a small amount of apps installed. It's just some people have problems, for which there must be a same cause I think.

I did a little experiment this afternoon by doing a factory wipe in TWRP and flashing Xposed again. Guess what, no crash after booting into Android. Of course, I couldn't resist installing a handful of apps I so dearly need. Like AdAway :) A handful quickly became about 33 (/edit: more, maybe 50-60) and then I got my first random red LED crash and reboot. This was with NO Xposed modules installed and active. Just now, I uninstalled some apps to see how well it goes now. /edit: I'm now at 43 user apps, 174 normal system apps and 128 frozen system apps.

Also I was thinking about [MENTION=5458816]Mr. Schnabel[/MENTION]'s similar experience.

Could this be that in those 3 weeks you did install (a few) more apps until you hit a limit? And that after you started over you never reached that same amount of installed apps?

[MENTION=7190406]D_STROY[/MENTION], you still have the same random reboot issue as me, right? Can you check (with Titanium Backup or anything else that can do it) how many user apps you have installed?

If you can share some of your logs, this can help.

Camera works fine after rooting? The Album app crashes, but you can fix that by deodexing it or by freezing/uninstalling it.

FWIW, in my logcat from the 2nd boot that crashed almost immediately, from a few days ago, I had these crash logs:

[COLOR="Red"]01-12 13:57:08.635 F/libc ( 3667): Fatal signal 11 (SIGSEGV), code 1, fault addr 0x1c in tid 3688 (Signal Catcher)[/COLOR]
[COLOR="DarkSlateBlue"]01-12 13:57:08.753 I/DEBUG ( 644): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x1c[/COLOR]
[COLOR="red"]01-12 13:57:08.917 F/libc ( 1340): Fatal signal 11 (SIGSEGV), code 1, fault addr 0x8 in tid 1349 (Signal Catcher)[/COLOR]
[COLOR="DarkSlateBlue"]01-12 13:57:12.170 I/DEBUG ( 644): signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x8[/COLOR]

A small summary.

The cause of the crash/reboot issues is not the ROM (28.0.A.8.260) or the kernel (AndroPlusKernel v10), because people with the issue (D_STROY and Mr. Schnabel) and people without the issue (DHGE and killdozer56) are running the same ROM/kernel. It's unlikely the people with issues are running the exact same German customized ROM as me.

The issue only happens with Xposed installed. I have tried both v78 and v79 (sdk21-arm64).

It's not an active Xposed module, because I can reproduce the issue without any Xposed modules activated.

When I have a lot of apps installed, tablet runs fine.

When I have a lot of apps installed and then flash Xposed, tablet crashes after completing 'optimizing' apps. Each time. After the reboot, it will crash moments after the lock screen appears. Each time.

'Lots of apps' could be one specific app that is't playing nice with Xposed. If so, it's likely not a preïnstalled system-app, because then all Xposed users would have the issue. Unless fellow victims D_STROY and Mr. Schnabel run the same German customized R6A flavour of the ROM.

When I have a lot of apps installed and uninstall Xposed, tablet runs fine.

When I completely wipe the tablet, and then flash Xposed, it runs fine. Haven't tested this very long, because I install my apps one by one on a clean device.

As soon as I have quite a few apps installed, the tablet starts crashing/rebooting. Again, I'm not complete sure on this yet.

What set me on the wrong path initially is that soft rebooting is broken on the Z4 Tablet. It results in a crash which fully reboots the tablet. Soft reboots are often caused by SystemUI crashes. On the Z4T a SystemUI crash most likely will crash the whole system.

So as of now, I think the cause is either the amount of installed apps or a specific (user) app that doesn't play well with Xposed.