Why 2FAUTH box required on top of Left Column.

Howdies o/ Earlier today on my Server one member without admin rights received small window on top of the left column (where channels are) that has writing about 2FAUTH code required & rights missing. Then there's 'resolve' button' on that box. I know that server's Admin & members with admin role can see that box sometimes, but not others. I forgot to take screenie when member showed it via 'share screen' at DM.

I heard that it's a "Discord thing" & with that require users to have 2FAUTH enabled to login. I've never enabled it. For ex. there's couple online since this morning & we've chatted without them having it. Then couple hrs later one familiar member noticed it today there when logged in. So why would it appear there on it's own  :/ Assist Required. Thanks o/ Kindly: Fedaygin