Why can't I access gmail from multiple POP email clients?

Question

Google

The scheme is as follows - one mail, several clients collect mail using the POP protocol, and collect it through Thunderbird. The username is "recent:[email protected]" according to
https://support.google.com/mail/answer/47948?hl=en...
Until today, everything was fine, when suddenly on both clients Thunderbird became give an authentication error. When replacing the username with "[email protected]" everything works, but this option is not suitable for several clients, because. letters are downloaded only by the first client.
Enters through the web interface. I checked on another google mail, the result is similar.
How can this problem be solved, and why did it arise?