If you have an ad blocker, it might be interfering with the menu. Disabling uBlock Origin for this site fixed the problem for me.
For site admins: one of the default blocklists for uBlock and other ad-blockers (EasyList) catches the "?tag_id=" portion of the menu selection.
Thank you for working this out, was wondering why this suddenly happened.
Until the Tech Guy for the site is back and can fix this, I'd highly recommend disabling any adblocks you have for this site. We don't have adverts anyway, so it shouldn't be a problem. May pin this thread if this is a recurring issue.