When companies release something into to Beta, they are close to being finished, but want to find any issues that may have eluded them, or see just how back some known problem areas are when a full stress test is put on it. With the release of the Fallout 76 B.E.T.A. on the Xbox One today for those that pre-ordered the game, the feedback is starting to come in.
Initial reports are centered around login issues and account linked to profiles. So all-in-all, not bad for the first day, but I am sure more will come. Keep in mind that you can always hit up the Bethesda Support Official Page to research or report any issues.