Have you tried to monitor your all units sometimes hash rate drop due to overheating Bitmain units automatically increase or reduce the frequency and fan of the hashboard depending on their temp?
Better use a monitoring tool to find out what exactly happens to your miners, Bitmain has free monitoring tools that you can check here "
MAnagement tools"
Sometimes the pool is down If I were you try switching to another Sha256 pool so that you can check if it's due to the pool server.
You can try ViaBTC pool or try any other pools from this link
https://miningpoolstats.stream/