SharePoint issues in a multi-tenant organisation

Working for a business running a multi-tenant organisation.  We have a "global" SharePoint Online instance, which users from other tenants access via their synced accounts.  It's the only SharePoint instance in our business which all our employees can access, hence we use it for communications/collaboration etc.

Found a number of issues with SharePoint, including:

1. Some of the "out the box" webparts don't work, for example the org chart webpart
2. In search, when you are viewing the profile of a user, their image doesn't show.

The cause for both problems is that synced users have a weird UPN, which includes "#ext#".  SharePoint is not encoding the UPN to make it URL safe - hence the browser doesn't send the complete request to the Graph API (truncates at the first "#" character). 

This seems like a repeatable and fundamental flaw. However, I'm finding it literally impossible to report. The helpdesk don't seem to understand multi-tenant organisations, and try to tie you up in to endless calls to discuss the issue - until you give up.  Literally all that needs to change is to encode the hash characters to %23.

Is there a formal channel where bugs can be reported to the dev team?

In general, we've found a massive number of issues with multi-tenant organisations - not just with SharePoint - and I would advise anyone considering going this route to consider carefully.  Especially topics like licensing in a multi-tenant organisation.