I did mean trying to plug it into a linked hub as opposed to different ports on the pc - definitely worth a try. I've had this problem with keyboards for about four years now - they miss letters out and sometimes refuse to type at all if plugged in directly, and this is with several different computers, and Win7 and 10.
Don't even think about going back to XP. Have you tried W10? I know that it's attracted some adverse comment on many forums, but I don't think that much of it is very fair. MS have never given an operating system to virtually everyone before. They've only given an upgrade on then very recently bought machines purchased close to an OS release date. What we now have are many millions of people installing a new operating system, who have never done it before. Some were going to go wrong, but this time there's no tech support.
I waited a couple of months before trying it (from 7 because I really didn't like 8) and it has been virtually faultless. One start up utility didn't work and had to be re-installed, and last weekend I came home to find a machine that had updated itself had shut down (but it may well have been a power cut, had two today). One machine was a bit stroppy about installing a film scanner and I thought that it was W10's fault. I rolled it back to 7, which only took a few minutes, found that it wouldn't install because I was doing it wrong, did it properly and re-installed 10. It really is that easy. There are plenty of tips on the web showing what to disable if privacy is a concern.
Anyway my point is that you could try 10 out, see if your Bluetooth works, then decide whether you like it or not.