A couple of thoughts:
Would it be possible for someone to send you a copy of an affected world since you can't replicate it?
Since it seems to be tied to lag and loading/unloading chunks, could the problem lie with the specs of the machines we're running the game on? Maybe the Mojang dev machines are too powerful for the bugs to trigger.
Here's a copy of the world on my server, as mentioned:
https://drive.google.com/file/d/18-2aUXXTdsBh57Z1z9xzmiDd2Mn-tavE/view?usp=sharing
There are a lot of lighting errors in the walled town at -240, -2300.