I am using Thunderbird 91.3.2 (64-bit) on an Ubuntu 20.04 base Linux distribution (KFocus). I have 5 email accounts configured - 2 on Zoho, 2 on gmail, and 1 on yahoo. Just recently, after the initial retrieval of emails, it has stopped retrieving new emails from the 2 Zoho accounts. When Thunderbird first starts up, it retrieves all new emails form all accounts, but then will only update the 2 gmail accounts and the 1 yahoo account. If I quite Thunderbird and start it back up again, it will then retrieve all new emails from all accounts, and then again just update the 3 non-Zoho accounts. I have had all of these accounts for many years, and Thunderbird has always worked with all of these accounts until now. Any help/suggestions will be appreciated.

Thanks!