Probably not the reason, but worth to do a quick check:
Sometimes the update cache interferes, so if something's odd with updates - some module (or core) claims to have updated, but then...
The issue with checking for updates in the BackdropCMS dashboard makes website development and maintenance more difficult. I manage more than ten websites hosted by two different providers, one...
Comments
If it's in a field or a node body, you can use the Markdown text filter in this module:
https://backdropcms.org/project/markdown