Note how the problem files borders are in blue. Leads me to think that they were saved in Edit Sheet Format mode. Another thing to look at is your layers. Make sure all your layers are turned on.
Yes, that seems logical, but I have went and re-saved when the drawings are out of sheet-editing mode and I couldn't get it to update.
I've also gone into other drawings that display correctly and saved them during the sheet format edit but the thumbnails remain OK.
Where can I check what layers are displayed?
Thanks for your help
Open a drawing. You need to turn the Layer toolbar on. One way is to go to View on the Title bar, scroll down to Toolbars, Layer and make sure it is turned. You should then see this:
Click on the "stack of layers"
and you get this
In the OFF/On column (the glasses) check to see if anything is off. On the example above you can see that OBJ layer is off.
Windows could also be the issue. Do a Google search on "explorer thumbnails not showing" and maybe toggle through turn OFF visibility of thumbnails, restart your PC, verify that you can not see any thumbnails. Then go back in and turn ON thumbnails, restart PC and see if they all show.
Hope that helps.