is this once a day, after every new message arrives. perhaps you could actually describe what you are observing.

Mostly these sorts of issues trace back to faulty anti virus products. What are you using?

pretty much after every new message arrives

After 'Get Messages' there is a message displayed at the bottom right hand corner of the screen indicating the the number of messages which have been received. They are not displayed in the inbox pane They are displayed after the 'Repair Folders' option is ticked but are not displayed when I revisit the the inbox and only after the 'Repair Folders' option is used again. I installed Thunderbird about a year ago and haven't had any problems until a week ago. Nothing changed in my software environment that I am aware of. This seems to be a common problem indicated with a Google search, but without a permanent solution.