It really depends on how much debris or sludge is in the filters (some is normal), and what exactly the debris is. It could be that there was enough stuff in the filter to cause concern about too much wear somewhere in the system, and they shut down propulsion as a precaution. Could be a wiped bearing—happens in new construction.
They will have to get a sample to a lab to determine the source of the contamination...something they can’t do at sea.
Don’t know about this ship’s propulsion....does it only have one screw? Spent MANY hours cleaning and inspecting propulsion plant lube oil filters on my boat (submarine for you civilians) many years ago. Filters were actually mesh bags with magnetic inserts to catch any ferrous particles....bags were reused after cleaning and only replaced periodically.
Propulsion is through 4 X water jets powered by 36MW of gas turbines.
Shut down the defective unit, and make port at reduced speed. But that is not very dramatic.