Has there been a change to the merge process?
I have come across this issue several times in the last couple of months following merges by other users. If it was only happening with one user I would say it was a user issue but that doesn't seem to be the case.
Example: Family 1 has father John1, mother Mary1 and daughter Fiona1. Family 2 has father John2, mother Mary2 and four children including Fiona2. Someone (correctly) merges the two Marys but this is when it starts to go wrong.
What happened in the past was that the surviving Mary would have had two husbands called John1 with a daughter Fiona1, and John2 with four children including a Fiona2. It would then be obvious and easy to merge the two Johns and the two Fionas.
What happened now is that following the merge the surviving Mary only has one husband and one family, in this instance John2 and four children. There is no indication that there is more work to be done. Until the system comes up with "Possible Duplicate" suggestions, which it may not, there is nothing to indicate that there is another husband or daughter, and that the two Johns and the two Fiona still have to be merged.
John1 now has no wife. Fiona1 now has no mother. It looks just like Mary1 has been deleted, not merged. It's only by inspecting their Change Histories that you can find there used to be a wife/mother that was deleted by a merge.
I've now seen this three or four times this year. Has anyone else seen anything similar or know what the problem is?