thunderbid error in SmtpServer.sys.mjs when sending messages

Hi, My Thunderbird instances suddenly started to choke on sending emails to smpt.office365.com (not sure for others). Both my 139.0.2-1 and 143.0.1-2 instances have the same problem: 1. I click 'send' and TH is stuck on "Sending message" dialog box. 2. devtools shows error in console: 08:57:41.360 NS_ERROR_FILE_NOT_FOUND: Component returned failure code: 0x80520012 (NS_ERROR_FILE_NOT_FOUND) [nsIFile.fileSize] SmtpServer.sys.mjs:598 3. When I click 'Cancel' in dialog box from (1) then, 'Send' again the problem repeats. 4. When I wait for TH to give up and click 'Send' again message is sent successfully. Anyone sees similar behavior? Regards, Łukasz