Why can my clients no longer view a PowerPoint in a group meeting?

Question

I am delivering a Therapeutic Course to clients.

This is 2 hour video meetings weekly based around a PowerPoint Presentation.

The problem is:  patients who do not have a work Teams account (via their employer) appear to no longer have the permission to view a presentation in a group.                                                                                                                                                                  On Thursdays 13th and 20th April, all clients were able to click on the link in the invite, join the meeting and watch the presentation (presented via Powerpoint toolbar.

On Thursday 4th May and now today, everyone can join the meeting but only the people who are using Teams supplied by their employer is able to view the presentation and I appear to be additionally unable to share my screen.

This is cringingly embarasing and very unprofessional.

A ticket has apparently been raised with MS. This advises me I can 'expect a response in 8'.

That apparently doesn't mean 8 minutes and so I'm guessing means 8 hours????

Anyone know if this is something I may be able to address (or even maybe our IT dept may understand if I escalate above current person).

The next meeting is due tomorrow and I need to know whether to cancel