Hello, I thought this might be related to the transparent ender chests but I was told to open a new ticket,
I use item frames on chests to indicate what is in the chest, for my map chest I use a map that I screwed up and it is mostly empty, in 1.14 and in 1.15 pre1 the unexplored portions of this map were transparent and the leather of the item frame showed through.
Now in 1.15 pre2 the empty portions of the map now make the item frame transparent and also the chests behind it transparent rendering instead as the wall and celling behind it, almost like a hole through the chest, see attached photo. chest still works fine, just a strange appearance.
not a huge bug, not nearly as annoying as the transparent ender chest but something to be aware of, hopefully since obviously it is something that changed from 1.15 pre 1 to pre2 it should be easy to track down and kill.