API error responses generated by AbuseFilter and SpamBlacklist have changed, as announced here: https://lists.wikimedia.org/pipermail/mediawiki-api-announce/2019-September/000148.html (relevant task: T229539).
It appears that some WMF-deployed extensions have special handling for the old responses (ContentTranslation, Jade, MobileFrontend, Translate, WikiEditor). They should be updated, otherwise they will probably show a generic error message instead of a more specific one. I searched all code for 'abusefilter' and 'spamblacklist' to find them. UploadWizard also had matches, but it uses the upload API rather than edit, so it should be fine.