On English Wikivoyage, I have discovered that enabling the HeadAnchor gadget causes some unwanted text to be added to the default Reply edit summary. It adds "h-" at the start and the current datetime at the end.
Topic on Talk:Talk pages project/Replying/Flow
I can see the same problem here on mediawiki.org (you have to find a non-Flow talk page to test, e.g. my own discussion page). I filed a bug: T281488. I'm not sure yet if it's a problem with the reply tool, or with the gadget.
@Nelson Ricardo 2500, this should be fixed. Please post here or on the Phab task if you still see this problem.
Thank you, @Whatamidoing (WMF). It does appear to be working now.