Preload works intermitetantly.

Preload works perfectly, preloading every hour.
When I go into the preload tab in settings, I can see the normal countdown.
However, occasionally I will go into the menu to check when the next preload is and there is no countdown to the next preload, and the preload is not running automatically.
Like its paused somehow.
The only way to get this working again is to click ‘update’ without changing any settings.

Any ideas?