Yeah my server is having this issue now as well. Its something to do with naturally spawning Concavenators.

We can hit them with C4 or rockets perfectly fine, it comes up, but then won't go back down. We've tried skiffing it to controlled locations and attempting to put different scenarios around it (new environment, leaving agro). Its naturally spawned Concaventors that are bugged. Not only that but I could not do any tranq to it at all, no tranqs took effect.

I tested this earlier today. Spawned one with Admin Commands, attacked it with c4. Did its normal thing and then returned to under sand like expected. Also attempted to tranq, and it worked effectively.

Conclusion: unless you want to get real lucky with a 1 time shot (aka make a 2h x 2L x 1w) hallway and put c4 in the middle and have it chase you into the hallway to blow it successfully, your going to have to spawn them in for real acting ones.

Still looking for fixes