I have some active jira customers being unable to access their accounts to create/check tickets. When checking the organisation of the teams, the individuals appear to have active accounts but when selecting their profile the directory is unable to find them.

Having directed them to reset their passwords they are unable to do so, I have moved onto resending them an invite to join jira again.
Is there a reason as to why this may be happening? and is there a more efficient way to resolve this issue in the future?
Thanks.