Presenter screenshots magnified and off center

Hi, I've just started using Presenter recently, and I've been able to work with it without many problems.  But in the last couple of days I've had trouble with using the screenshot function.  

I've attached the way one problem presents - when I tried to use it to capture this screen all I got was a black photo, but with the address line for the site at the top.  At other times the screenshot is magnified and offset. and I've never seen PowerPoint do this alone.

I'm using MSOffice 365 ProPlus, version 1708, on a ThinkPad with 156GB free space. It's a 64-bit machine.  Any help would be most appreciated!