I have seen where all ports go off-hook when they have a common button programmed on the key map such as a line button or phdn. Staying stuck in that state could be explained by no disconnect supervision if it was a line button that caused them to go off-hook in the first place. The underwater thing could be a voip/network issue. Make sure QoS is configured properly. Just some things to check.

There are more recent software versions for both systems.