It also seems to happen when I am on the surface. What happens is that nothing will take damage. This results in a ton of enemies staying on the surface during a wave fighting five ants. This could allow me to build up my forces if I was not fair. It seems to happen in all levels and gamemodes. Even the formicarium has this glitch.
Could you record a video of this behaviour? I have tried to replicate it myself but I am getting nowhere. Additionally can you check you have the most recent build of the game (in the lab menu screen should say 0.1352 in bottom left). I have just released a patch today.
There was an optimisation we introduced ages ago but had to remove (which basically stopped animations you could not see) which sounds like what you describe. We did as I say remove it so I am not sure what is causing the problem here. Maybe try verifying your files on steam make sure something has not gone wrong there. This is the only report I can see of this issue.