Mac Mail "Downloading Messages " thousands mails always on startup
Running
macOS Big Sur 11.2.3 (20D91)
An odd issue has arisen wherein my Mac Mail is constantly displays a "Downloading Messages" message when no new emails are being downloaded. It often displays that several thousands messages are being downloaded.
PS
I tried trick with sorting draft "On My Mac" in "Mailbox Behaviours", didn’t help and starting Mail app with shift as well.
Thank you for help.
MacBook Pro 13″, macOS 10.15