After some time for example playing at night then connecting at morning, some chunks are missing microblocks.
Server restart helps, reconnecting did not help, blocks are just missing, there is no collison.
No error logs, only some warrning probably not related to this problem.

LOG: https://pastebin.com/CnYFgEVF

Problem exists on:

Forge: 1.12.2-14.23.3.2655
FMP: 1.12.2-2.4.1.57
PR version: 4.8.6.66

AND

Forge: 1.12.2-14.23.3.2698
FMP: 1.12.2-2.4.2.58
PR version: 4.8.6.74

Update: It is happening on chunk loading/unloading.
If you go far away from placed microblocks and then return to this place, some chunks are fixed and some are missing microblocks.

Duplicate of #1277