I am a sysop on fr.WP and found out that when deleting revision, the wikitexteditor automatically launches itself (after submitting the revision deletion), rather than showing the confirmation message. Tried with &safemode=1, same thing.
Topic on 2017 wikitext editor/Feedback
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I wonder whether this might be the same (underlying) problem as phab:T176022. If so, then it might be fixed soon. I've pinged you in that task.