Print layout of multiple maps revert to one identical map after save as image/zoom

I have a map with 8 graduated classes. I have created a print layout with 8 separate maps – one for each of the classes. I used "lock layers" to ensure that each separate map displays just one of the classes. Everything looks fine, however when I try to export the image (or PDF), all of the maps change to reflect the one I changed most recently and I end up with 8 identical maps. The image file does not save the different maps. I have updated to the most recent version of QGIS (3.10.13) in Windows 10.

Edit: it seems just zooming in or out of the print layout also causes this problem