I still use the UA-1G audio interface. The driver hasn't been updated in years. Sonar performance has really degraded in the past few months especially after that Windows 10 update caused so many issues. I'm wondering whether it may be linked to my audio interface. Is anyone still using the UA-1G and if so, are you seeing any performance issues?

You can expect issues if you use older equipmment without w10 support. The driver and the OS need to work smoothly together. The interface is the heart of your system and the driver is the most important factor.  I'd start shopping. Check out the new Tascams, for me it's the UH 7000 or better yet, something from RME or Motu.  

Cactus Music
You can expect issues if you use older equipmment without w10 support. The driver and the OS need to work smoothly together. The interface is the heart of your system and the driver is the most important factor.  I'd start shopping. Check out the new Tascams, for me it's the UH 7000 or better yet, something from RME or Motu.  

That's what I was fearing!

The UA-1G was only USB 1 and with unbalanced I/O, so if that's done the job for you, the good news is just about any new sub $100 interface will still be a big improvement.
 
I can wholeheartedly recommend the Steinberg UR-series. Solid build and drivers, they start at $100 (the UR12).
 
The Focusrite Scarlett Solo and M-Audio 2x2 are also at that price point.  Of course, you can spend more, so let us know your budget and I/O requirements, and we can give you some more recommendations.

Thanks again to all you fine folks for your feedback. I finally pulled the trigger on a Focusrite Scarlett 2i2 2nd generation. I think it will serve me well!  Merry Christmas to me!!