thunderbird keeps forgetting my email account passwords

I have 10 email accounts I have to monitor. When I set up Thunderbird on Windows, I entered all the account info and the passwords. I checked the box 'use password manager'. This worked well for a few days. After several days, I started the app again and it asked for every password again. I entered all the passwords again. This happened several more times. I sought help for the bug, but found none. Someone suggested deleting password database files in the Thunderbird data folders. This did not help. Someone else suggested that CCleaner may be deleting password data files, so I added the entire Thunderbird data folder to the scanner exclusion list. Yes, this may be a security risk, but I need this app to work, as I have not found any other app that even begins to get the job done. Ready to start looking for another email app now, unless someone can fix this problem. It is not reasonable to expect me to lookup and restore 10 passwords every time I check my mail.