I was thinking it was a generic issue, but it's the BF UV-5R and Win 10.
I did run across some information that helped. The filename MUST not be, "Generic CSV xxx" as the filename to load. It has to be, "Baofeng xxxxxx.img", otherwise it won't upload.
The solution is to save the radio-downloaded file, then open your self created file with your personalized frequencies resulting in two tabs in CHIRP. Copy your frequencies form your file into the new one, then "save as", retaining the first part of the filename.
Yes, the file name, the radio model, etc. must be correct. Glad that you found information to help you out.
I have a couple of the UV-5R hh and they are fairly decent transceivers.
One important note: when first running your transceiver on Chirp, ALWAYS upload an image of your radio firstly, ALWAYS. Before downloading anything to the radio. That way you have backup should there be a fault occur.