Sylvia,
I agree there might be a RAM or SSD problem - however I was not able to prove it (Memtest returns no errors at all, Intel SSD toolbox also says everything is fine). A couple of other users have also reported similar issues, but they seem to have disappeared with the latest drivers/BIOS update.
Will try to obtain another RAM to test with, and there are still BIOS updates 0025 and 0026 pending to be applied, perhaps that will also help (since there was some graphics controller updates in each BIOS update).
I will post back after vacation (beginning of August).
Thanks for the help/comments,
/HarveyV