latest.log
the carriages just disappear, no collision or visibility.
this is with optifine and Create - mc1.16.3+4_v0.3.jar.

and Optiforge

Thank you for the report. This is pretty serious

latest.log
logs without optifine

issue persists without optifine

Yes. The serialization is not symmetrical, it'll be fixed in 0.3a

i would guess this is the issue https://pastebin.com/JYq4G24g