Unknownreported this bug
I have seen some people having the same issue with invisible mobs. The mobs in paper 1.20.2 will only be visible to players who using 1.20.2 and will be invisible to the lower version. don't sure if Ticxo can do something about it or needs to wait for Via update.
I have updated Viaversion and Viabackwards to the latest dev build, still not fixed. [Legacy attachment omitted]
server: paper 1.20.2-297 MEG4: R4.0.3 ViaBackwards: build 349 (in Discord someone said 330 work, but not for me) ViaVersion: build 739