The Narayana TM maintains a config bean containing CMR JNDI names that the recovery system uses to complete transactions that use CMRs.
When a WFLY CMResource service is stopped the service gets the list of CMRs from the narayana config bean and removes the resource (that the service was using) from the returned collection. But it only removes it from a copy of the list so narayana will continue to treat the resource as a CMR.
The suspicion is that if the resource name is reused as a non CMR resource then the recovery system may confuse it as being a CMR. Also since CMR records are processed before others this will cause it to be processed first. And worse if there end up being two CMRs left in the list (due to this bug) then narayana will throw an error when the second one is enlisted in a transaction (since there can only ever be one CMR per transaction).
With regards to the priority of the issue, I doubt this will result in data loss/corruption but the bug does have the feel of being a blocker.