Zoom Minimizing Main Screen When Sharing

Hi. I run a few distance learning classrooms. We run Zoom on Microsoft Surface computers with two external monitors. So, three total monitors. Instructors share Powerpoints via with Zoom in dual monitor mode on the external monitors. This has worked fine for years. Now, when the Powerpoint is shared, it minimizes the main Zoom box, taking the audience out of view and it moves the floating control bar over the Powerpoint. This makes dual monitor mode unusable. So, my workaround has been to disable dual monitor mode for now. I have checked every setting and made sure the display settings on the computer have not changed. Has anyone experienced something like this?  Thank you.