When you restart a node on the DMQ bus, it can trigger memory usage on the other nodes since they will start to do a SYNC and send one DMQ message / contact
It could be that one node in the DMQ bus is restarted and not answering DMQ messages ?
Few ideas :
You could search you trace, maybe you will find the DMQ sync requests ...
You can also confirm significant increase in active transactions.
Verify the state of the bus :
kamcmd dmq.list_nodes
Verify the amount of contact on each node (confirm that the cluster is healthy)
kamctl stats | grep usrloc | grep contact