Again just guessing, but you're using ANIM::SONICPLAT, but I don't see any explicit calls to jjOBJ::determineCurAnim or jjANIMSET::load, the two ways of manually loading an animset. So I suspect you're loading the animations by placing one or more Sonic Platform events in the level... but those don't work in multiplayer unless they're set to MP-Only.

Alternatively, use ANIM::CUSTOM[1] instead (after an appropriate allocate method call), since it doesn't look like you're interested in Sonic Platforms as Sonic Platforms?

(None of the stuff you're doing in onMain needs to be done every gametick either, fwiw.)