The questions tagged (algebraic geometry) are no longer displayed in blue on my screen, although that tag is among my favourite tags.
I tried (through the edit) to suppress that tag from my favourites and then reinstall it, but to no avail.
The other tags seem to be ok, so that questions tagged (algebraic geometry) and some other favourite tag are displayed as usual.
Only questions with the unique tag (algebraic geometry) pose a problem, like this one for example. Can something be done ?
Everything works again: I have added the tag (algebraic-geometry) whereas earlier I had the tag (ag.algebraic-geometry).
What exactly does the prefix "ag." do (or in my case undo...) ?