In MergeTableRegionsProcedure, we close the regions to merge using UnassignProcedure. But, if the RS these regions on is crashed, a ServerCrashProcedure will execute at the same time. UnassignProcedures will be blockd until all logs are split. But since these regions are closed for merging, the regions won't open again, the recovered.edit in the region dir won't be replay, thus, data will loss.
I provided a test to repo this case. I seriously doubt Split region procedure also has this kind of problem. I will check later