I had the same problem when programing some NPCs the idea that I got to have them push each other a little bit when they collide(not enough to stop their movement but enough to make them not to fuse together), but sadly I never tested if it really worked so look into it but don’t be too optimistic.
Ps: You can make the push stronger if the NPCs closer to each other but again it can create some problems so do check if its something that you want.
Pss: If you do try this try to shutdown AI CC to see if it works better without it as well.