Gmail "Opened in one more location", something wrong?

Question

gmail

When you log into gmail, the lower right corner shows "open in one more place", despite the fact that the device / browser, etc. - unknown, login comes from my IP address, +/- at the same time. VPN, Tor, and this and that - it doesn't matter, the result is the same. With live usb Ubuntu - still the same result. In the mail settings, POP and IMAP are disabled, forwarding of letters to another address is also disabled. In the security settings of the google account - login from only one device - mine. I log in only from my computer, no smartphones. Login with two-factor authentication. Passwords are changed with a preliminary exit from all sessions.
With each new session - "open in one more place" and "unknown" why.
Firefox browser, Ubuntu 19.10 OS.
So: what could be the matter and how to get rid of it? Perhaps I missed something, but who can come across?