That's a really bizarre glitch. Have you tried quitting the game, restarting and choosing to start at the mirkrooms see if it fixed it? I have an idea where the bug might be, but I am not sure if I will be able to replicate and fix it.
In the meantime try to see if a restart fixes it, otherwise if it is consistent tell me how many players or what player slot you were using.
EDIT: also! Do the platforms explode or vanish? Like they just disappear instead of going boom.
Sorry for the trouble and thanks for reporting!!