I suspect there isn't much to be done about this, and there is a workaround anyway (see below), but I'll mention it here just in case: TeamPneumatic/pnc-repressurized#290

I think what's happening here is that PneumaticCraft's Spawner Agitator's calling of TileEntityMobSpawner#isActivated() via reflection (https://github.com/TeamPneumatic/pnc-repressurized/blob/master/src/main/java/me/desht/pneumaticcraft/common/semiblock/SemiBlockSpawnerAgitator.java#L42) isn't compatible with Foamfix's injection of an overridden MobSpawnerBaseLogic class.

It can be worked around as described in TeamPneumatic/pnc-repressurized#290 (comment) so it's not critical, but I thought I'd mention it. Feel free to close this if you don't see an easy fix for it :)