Isn’t it the combination of the symptom and the workaround? E.g. you have a blue screen with Error #1234. We know that Error and we have a workaround – e.g. re-boot. Unfortunately we don’t yet know the root cause.
This is why I advocate early raising of the Known Error. The Known Error can be useful before one knows the root cause.
If your ITSM systems separates Problem and Known Error (implements them as separate ticket types), then my advice is to raise both at the same time. Use the Problem ticket to manage the Root Cause Analysis and use the Known Error to manage the work around. This is especially useful if the work around is being worked on by a different group to the one coordinating the RCA.
ITIL Expert’s take: Raise Known Errors early. They can be useful well before the actual root cause is known.