Basically, if two duplicated references merged, the merged reference won’t have the citation key with correct format. I notice this issue back in the beta. It still hasn’t been fixed.
For example, if the correct citation key should be “ali2018”, and merged one becomes “Ali2018018”. I can see the number part, but I don’t understand why it becomes upper case, since my setting is lowercase. It seems that the app merged the citation keys, which doesn’t really make sense, instead of setting the citation key based on metadata as what the app does when adding a new reference.