Cubase 10 not recognizing its own .cpr files

After setting up an empty project with many instrument tracks that I then disabled to be used/enabled later, Cubase Pro 10.0.10 apparently saved the .cpr file corrupted. Neither 10.0.10 then 10.0.15, nor 9.5.41 would recognize the .cpr files or the .bak files. I think it may have had something to do with Native Instruments Kontakt instrument tracks. It seemed to happen after adding many Kontakt tracks (15 or 20 maybe), or a certain instrument track (not sure which) was added and then the project was saved. This happened twice after I tried to build the project. It saved and opened properly until the breaking point in question. I then went back to using Pro 9.5.41 out of frustration and concern that this might be a true bug. This issue was not listed in the 10.0.15 bug fixes. I’m sticking with Pro 9.5.41 for now until this is checked out by others. Sorry, I won’t spend another four hours trying to replicate this problem. Too much of a waste of my time already. I’ve been using Cubase since version 4 so I’m not a newbie just clicking randomly and hoping for results. This is a Cubase problem, or a Kontakt compatibility problem. I have the latest of both programs - Kontakt and Cubase Pro. I also have all the latest Windows 10 updates on a 4.4 GHz machine with 32 GB of ram. I’ve also rescanned all the VSTi folders. I’d like to get back to Pro 10 ASAP because I paid for the upgrade and I like its new features. Thank you for any feedback, comments or suggestions. Doug