How to debug videobridge calls - freeze on 3+

Cleary having an issue now with calls going to 3+ participants. P2P is fine, and some calls work fine on 3+, but more often than not the third participant (& 4th, 5th, etc) causes all videos to start freezing, skipping, etc. Not entirely sure which resources to look into first. Server CPU and network throughput is nominal so I’m looking at config options to try tweaking. Capped resolution to 720 already.