<figure-inline> tags for inline images were introduced in a relatively recent version of Parsoid (September 2017); previously they were wrapped in
This issue sounds like something that might happen if you updated your VE (so that your new version of VE generates
<figure-inline> and expects Parsoid to handle them), but not your Parsoid (so your old version of Parsoid doesn't know how to handle them yet and outputs them as-is to wikitext).
The solution is probably to upgrade your Parsoid, or if you can't do that (especially if you installed from a Debian/Ubuntu package, I think they are not updated very often), you'll have to downgrade your MediaWiki/VisualEditor :(
(Relevant commits for context/dates: https://gerrit.wikimedia.org/r/c/mediawiki/services/parsoid/+/376046 https://gerrit.wikimedia.org/r/c/mediawiki/extensions/VisualEditor/+/371074)