Collisions seem to compound lag-related problems.
Since latest update maps which involve many collisions (i.e. ragdoll collisions in Shotgun Madness or moving geometries in Equilibrium) seem to make lag related issues more severe. Noticed on EU servers with players from 50ms - 300ms pings.
Mostly causes stretched ragdolls, player desync, players not respawning properly or player bodies not being cleaned up on round start, and slow map round endings which can lock up server prior to mapvote.