@murdos - sorry, I don’t have a GitHub account to report this properlly. The MB server update that was done today has caused a hiccup on your Musicbrainz UI enhancements script.
That is in Vivaldi Browser on Win10 with no other scripts running on that page. Toggle your script off and the page shows ISRCs again.
I assume it is because the server hamsters have fixed this old bug:
Last week that would have been a long line of ISRCs on one line making the formatting go mad. Line feeds have now come back. 
Updated: Looks like this will be the change: [MBS-12334] Collapse ISRCs and ISWCs when there are too many - MetaBrainz JIRA