Google has added a new AMP error to the Search Console AMP enhancements report for disallowed !important CSS qualifier. This was added back on January 19, 2021 and as a result, you may see an increase in the number of AMP errors reported after that date.
Google wrote “Search Console has added a check for a new AMP issue type: disallowed !important CSS qualifier.”
Google explained since it added this new AMP issue type, “as a result, you may see an increase in the total number of AMP issues reported for your site.” “This doesn’t necessarily indicate new errors on your site, only that we are now checking for this error,” Google said.
You can access your AMP enhancements report in Search Console over here to check it out.
Forum discussion at Twitter.