User Name Generation rules - Special character issues

Content

Hi,
we chose as the "User Name Generation Rule" the option "FirstName.LastName". The username is automatically generated once HR hires the employee in HCM.
We are experiencing several issues for several users who have spaces or special characters in their FirstName or LastName.

I summarize them below:

1) Spreadsheet Loader doesn't work
2) Bell Notification Sync doesn't work (and the user can't access In-App workflow notifications)
3) SSO with PBCS doesn't work (username in PBCS can't have special characters)

How is that possible that the automatically generated username causes theses issues?
We have no control on how the username is generated since we chose one of the delivered rules.