MLSS Performance Problem

Hello team, I am running MBR system constituting Mbr module, Aeartion module and Aanoxic module. This is an 8 train system. The challenge is that one of the trains has literally got no MLSS, reads about 100-500 mg/l against a target of 7000 mg/l. What could be the problem? What established way exists for improving MLSS in activated sludge systems?