Sorry, should have included that this happens when I start Thunderbird and I am downloading new messages. I usually have about +60 messages to download. I am importing the messages from a couple of MSN Outlook accounts.

Try to start Windows in safe mode with networking enabled. - Win10 https://support.microsoft.com/en-us/help/12376/windows-10-start-your-pc-in-safe-mode

Still in Windows safe mode, start Thunderbird in safe mode. - https://support.mozilla.org/kb/safe-mode

Does the problem go away?

Please post your results

Thank you Christ1 - Thanks for your response. I started Windows 10 in Safe Mode with Networking and then started Thunderbird in Safe Mode. I did not encounter the problems I had been having. I do want to see what happens next time I start without Safe Mode.

Does this mean one of my add-ins is causing the problem? If so then I should probably turn off my add-ins one by one and see if that fixes the problem. Is that the correct approach or would you have another suggestion.

I would not think I should have to use Safe Mode all the time.

Thanks again

> I would not think I should have to use Safe Mode all the time.

Correct. Safe mode is a test, not a solution.

Your next test is start Windows normal and start Thunderbird in safe mode. If problem goes away then an add-on may be causing the problem. Otherwise, something started during Windows startup (like Kaspersky) is causing the problem.

Either way, feel free to post your list of add-on installed. And Please post your results.