I’ve encountered this three times in two days, two of them in the last round of a solo run (one in Cistern, the other in Slaughterstar). Basically, some lone enemy, possibly a flying enemy but it could literally be anything, gets hidden behind level geometry and cannot be killed (at least, the few times I’ve attempted I can’t do anything with it).
Needless to say this is extremely frustrating and a casual perusal has shown this has been a problem for quite some time.
Edit: This is supposed to be on PS4 support but I cannot be bothered to figure out how this forum system works so if a mod wants to transfer it, please do so. A search for support only gave me the option for PC.