Missing motion triggers sometimes

I have noticed it as well from 5.4.8.X on having issues with showing it triggering yet an alert isn't showing up.

If you are not running DS, then rollback to an earlier version?

It is not uncommon for people to get to a stable version for their system and setup and leave it there. No real reason to update it unless you want to use a new feature that was added.
 
Same here.