Bungie names this code but does not publish the wording it prints on screen, so we quote only the code itself: WEASEL. Any site showing you an exact message for it has written one.
This one genuinely goes both ways, so the first job is telling which you are looking at.
Bungie has every core Destiny 2 service switched on
Bungie's own description is blunt about its breadth: “The WEASEL error code is an all-encompassing error message that is usually an indicator that you are experiencing a general networking issue.”
Two specific cases hide inside it, and both are worth knowing. On cross-save, Bungie states: “Cross Save does NOT cause WEASEL errors. Players who attempt to log in to multiple platforms simultaneously while Cross Save is enabled on their account will receive a WEASEL error on which ever platform they logged in on first.”
And on bans: “If a player is in an activity when a ban is applied to their account, they will be returned to the title screen with a WEASEL error.” That is a rare case, but it explains the reports of WEASEL that no amount of network work fixes.
If everyone is getting it at once, it is Bungie's side and the live status above will show it. If it started the moment you signed in on a second platform, it is cross-save and you need to sign out there. If it threw you out of an activity and you now cannot get back in at all, consider that an action may have been taken on the account. Otherwise it is your network.
Operator documentation: help.bungie.net. Bungie documents its error codes in a public directory of over 300 articles. Those articles describe causes and fixes and never quote the in-game dialog, so neither do we. WEASEL is documented as having split off from CENTIPEDE, which is why searches for one often lead to the other.
Bungie's own description is blunt about its breadth: “The WEASEL error code is an all-encompassing error message that is usually an indicator that you are experiencing a general networking issue.”
This one genuinely goes both ways, so the first job is telling which you are looking at.
Start with: Use a wired connection. Bungie strongly recommends Ethernet over Wi-Fi and puts it first. For a game that makes peer connections, packet loss matters more than bandwidth.