Did you run the Microsoft Windows10 COMPATIBILITY TEST prior to your Win10 upgrade? If you did, it would report any application that is not compatible at the Registry level and would not run correctly or at all in Win10 post-upgrade. If the application passed and was not reported by the Win10 COMPATIBILITY TEST, then Microsoft tells you that application conforms to both OS, library, and Registry guidelines to run in Win10 mode.
You can also contact your 3rd party developer and ask them if they have re-written their application to be compatible with Win10 or not. If they have, and it doesn't work, you may have a hardware problem with that computer you are testing the application on. I would suggest you run MEMTEST & SEATOOLS on that computer to rule that out. You mention that you have upgraded this computer that you are testing the application with from earlier versions of windows back to Win7. That means that this computer is about 7 years old, and is quite prone to hardware failure. If hardware testing passes, and the problem persists, I would try on at least 2 other working Win10 computers. If the problem persists on multiple Win10 computers, that would suggest your 3rd party software developer didn't do their job properly! Software developers have access to special tools to correct this problem, and if they are an MSDN developer subscriber they can get access to those special programming tools to help debug their application and correct the problem.
Also, did your 3rd party developer remember to submit the Win10 version of his application to Microsoft for WHQL testing? If not, it's not Microsoft certified to be compatible with Win10, only certified as compatible by the developer. That's why it's important for you or him to run the Win10 COMPATIBILITY TEST. If the developer has a boxed retail version of the product with a Disc or USB stick in the box, and it's got a MS Certified Win10 sticker on the outside, it's been tested by Microsoft, or if the sticker is on their website; such as a "Microsoft Platinum Partner" or some such.
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