Have you checked your Kentico cache settings under Settings > System > Performance? Sounds like maybe someone upped the caching which could cause this issue. You have multiple types of caching that could look at including server, client-side and output caching. You can try turning off caching completely to test and see if that fixes the issue. It will cause some definite performance
I would also check the System page to see if you see a large amount of cached items, memory usage or garbage collection. Those could indicate an issue.
Lastly I would check the event logs to make sure the page is actually getting checked in and there isn't any issue on that side or potential other errors that could give you an indication what is going on.