Judging by the information posted on the Reddit forums, Bethesda began to actively ban those who use Fallout 76 mods. Even those who used harmless modifications that adapt the game to ultra-wide monitors were hit.
Bethesda has already announced that it will not tolerate cheaters in the game. It can be understood that the developer does not welcome third-party modifications in Fallout 76, which is essentially an online game. However, one can understand the discontent of users who are accustomed to the fact that games from the Fallout series could always be modified.
Perhaps Bethesda is just testing a new anti-cheat system. The situation may change with the appearance of private servers in the game.
Link to news: Players are getting banned