This exact same thing happened to us. We have hundreds of meetings going back a couple years with no issue, recordings + transcripts. May 15th was the last day we got transcripts, everyday since no transcripts.
It seems quite clear that someone has broken on the Zoom side of things. We filed a support ticket and it was escalated but with no confirmation of the issue before being closed with the following message:
Our Technical Support team assists with product-level defects. We have confirmed this issue is configuration-related and not within the scope of your account’s Developer Support Plan, as such this case will be closed.