Updates inconsistently missing from Updates page and no update count bubbles in admin menu

[galbaras]

Until a few weeks ago, when there were X outstanding plugin updates, the Updates page showed them all, and the Updates and Plugins items in the admin menu showed a red bubble with X in it.

Now, when I log into WordPress, there are no red bubbles, and navigating to the Updates or Plugins page causes the bubbles to reappear, but the respective page may or may not show all the outstanding updates.

Sometimes, forcing the update check results in a full list, and sometimes, simply re-navigating to the same page completes the list. But sometimes, some updates disappear for no apparent reason.

I suspect this is related to having a premium plugin update on the list, but can't be sure. It just seems like partial lists contain a premium update, and often, it's one of those missing.

I've ruled out browser caching and there are no console errors or PHP error log message that could be related.

[galbaras]

BTW, applying updates seems to be the reason for the disappearing bubbles. Once either Updates or Plugins is visited, the bubbles continue to appear, even if the number in them is incorrect.