There is an option in the debugging page for displaying messages (or not). They will still be logged even if not displayed.
Ok... I just meant a quick overview of the setup and how your cache was configured. So, it sounds like you are using the default setup. Have you changed anything in your caching setup? How is your 'moodledata' file area set up. Is it local storage or something else? Could there be - for example - file locking problems?
I completely disagree that this is a common issue in normal use. Most reports are "I upgraded and....".
Have you considered using a dedicated cache server - e.g. memcached?