Update: https://signatures.toolforge.org/ seems to misclassify people with & and ' (and maybe other characters) as having a mismatch between the username and custom signature. Perhaps ~10% of the people contacted on enwiki recently were false positives.

It wasn't the characters themselves that was the problem, it was people using HTML entities like &.

That makes sense. It should be easy enough to strip those names out of the lists by hand. There aren't that many of them, and I think it only affects the "mismatched" error, which isn't the most common.

They're being correctly parsed now, and I've re-run the report so the bulk lists should be correct as well.

You're wonderful, @AntiCompositeNumber. Thank you.

Mismatched user names

In April 2021, we sent messages about mismatched account names to 140 editors with custom signatures. A spot check of 16 editors from the larger Wikipedias showed that 25% of people had corrected the problem two weeks later. There were no questions or comments from these editors. Many of the editors with this problem do not edit frequently, so it is likely that some editors will correct their signatures later.

@Whatamidoing-WMF Please triage this task again.