Fusion - Locked Accounts - Any known processes/ bugs that lock the accounts ?

Summary:

With a user population of approx 6500 employees and Single Sign On enabled we are seeing around 2-3 Fusion user accounts being flagged as 'locked' daily.

Content (required):

We are trying to get to the bottom of this to determine if this is an end user training issue, mobile device issue or if we have an issue with the system that is locking the accounts.

We have Single Sign On set up in IDCS for Fusion ERP/HCM

Fusion HCM accounts are set with future expiry (so expired accounts shouldn't be cause of lock)

IDCS is not reporting failed logins so I don't believe it is caused by user entering user name /pwd in the chooser screen.