According to other answers posted here on the subject, the update should take place at 3:00AM UTC, every 24 hours. I find it very common recently to not run for 2-3 days straight (or maybe I wasn't paying attention before).
I suggest a simple feature to add on StackOverflow, to let users know what time their tag score was last updated. Consider how Tags tab currently looks in your profile:
It can look like this:
Color can be adjusted to be grey or otherwise make it less visible, so it does not distract a user, but remain there, if you need it. No more tag score anxiety.