Error at O365 sign in: AADSTS51004: To sign into this application the account ___ must be added to the directory ___

We have a federated domain using OneLogin cloud directory for Identity Management.  There is no active sync between AAD and Onelogin, so we synchronise the 2 directories by manually adding the Immutable ID to OneLogin Cloud Directory.

Our user is successfully authenticated by OneLogin, but cannot access O365.  

Error message:   AADSTS51004: To sign into this application the account <ImmutableID>  must be added to the directory ___?

This issue just occurred as of Thursday 17th Aug.  Before this user worked perfectly.

Help would be greatly appreciated.