After reinstall user in Entre Connect, the O365 fails for the user

Question

After reinstall user in Entre Connect, the O365 fails for the user

Josselyn Boudett 0

UTC Date: 2026-02-12T04:02:28.663Z
Client Version: 20260130003.07
BootResult: fail
Back Filled Errors: None
err: Error: 401
esrc: StartupData
et: ServerError
estack: Error: 401
    at Object.w [as createStatusErrorMessage] (https://res.public.onecdn.static.microsoft/owamail/hashed-v1/singleCss/scripts/owa.mailindex.b3274fb9.js:2:8809)
    at https://res.public.onecdn.static.microsoft/owamail/hashed-v1/singleCss/scripts/owa.mailindex.b3274fb9.js:2:41447
st: 401
efe: PN2PR01CA0120

Sridevi Machavarapu 22,810 Reputation points Microsoft External Staff Moderator

2026-02-12T06:41:03.88+00:00
Hello Josselyn Boudett,

After reinstalling Entra Connect, synchronization issues can sometimes affect user attributes, licenses, or mailbox provisioning, which may result in 401 errors in O365/OWA.

Could you please check and confirm the following:

Whether the affected user is syncing correctly and showing as healthy in Entra Connect.

If the user still has the required Microsoft 365 license assigned.

Whether the mailbox is present and active in Exchange Online.

If there are any recent sync errors in Entra Connect.

Additionally, please try performing a full sync and have the user sign out and sign back in after clearing browser cache.

Let us know the results so we can assist you further.
Sridevi Machavarapu 22,810 Reputation points Microsoft External Staff Moderator

2026-02-13T05:09:42.9466667+00:00

Hello Josselyn Boudett,

Could you share above requested details that helps us to troubleshoot this further?