Ignore my previous two comments. It was a server host issue that caused the glitch. You can re-close the bug.
It wasn't MC-161823. The chunks got reset to their default terrain. MC-161823 has the chunks being mixed together.
I believe it still is an issue. A server that I play on had this happen to a bunch of chunks. It was in 1.15.2
chairpop
Ignore my previous two comments. It was a server host issue that caused the glitch. You can re-close the bug.