Please raise a support ticket, and attach your scribe to the ticket so the team can take a look.
In the meantime, you can also render your scribe into a video and then embed the video into PPT (https://support.office.com/en-gb/article/insert-and-play-a-video-file-from-your-computer-f3fcbd3e-5f86-4320-8aea-31bff480ed02)
I decided to try and export one of my scribes into PowerPoint. I could see the progress bar reach the completion of the export, gave the pptx a name, and selected where to save it. The pptx file is not there, however. I've tried this now three times and I don't know where that pptx is, if it was generated at all.
Maybe somebody here has more experience exporting scribes into PowerPoint, and I will greatly appreciate any insight you might have!