As raised in MBS-2681, if you have two artist entries (for a VA release, normally) that differ only by leading or trailing whitespace it will ask you to add missing entities twice on the AME tab. e.g. Because of the whitespace, it's not apparent why it's asking you to add-or-select the same artist twice. I believe such names get auto-trimmed by the system when entering edits, so doing this prior to the AME step shouldn't be an issue, I don't think?