When opening Sonar Platinum, more times than not, I'll get a message that there isn't an audio interface available.
That means I have to turn off the Tascam, then back on, then either closing Sonar and re-opening it...or setting Sonar to another driver driver setting, and then setting it back...all this is a good 5 or more minutes which is driving me crazy.
Also, after Windows decided to update to the current Windows 10 Creators update, there is an incompatibility problem with Sonar, so it changes settings to allow a "work around" ...butttt....while working in Sonar, all of a sudden there will be no sound at all...although the interface will still be in place like before, just no sound. 
Again, I have to go through the drill of rebooting sonar, hoping the tascam will be "available" and work properly...
Talk about a crappy workflow!!!! Any suggestions out there? Craig? I know you have this interface...
Thanks for any ideas! DannyJ

one more thing...this is worse with the new Windows version, but it was a problem before, just not as bad

Not claiming to be an expert, but managed to get a US-20x20 running fairly well in a small project studio. The drivers do not appear to be as robust as say RMEs, but it should be running better than what you're seeing.
 
I assume you have the latest fw and drivers installed. 
 
Windows updates continue to be a problem. I run this on Win 10 Pro with updates turned off. You may need to recheck any optimizations done for robust driver performance. (i.e. power settings, screen saver, etc.) There is a mention of an issue with the Windows Creator update but the workaround on their product page seems to address that.  
 
Is anything other than the Tascam listed in Device Manager > [your PC name] > Sound, video and game controllers? (Took some effort to kill a persistent video driver here that kept reinstalling itself.)
 
Plugged into a USB 3.1 port from the m/b, not a USB hub. That may make a difference. 
 
Latest practice in this project studio is to disable the network connections when running the Tascam.  

Might want to try running LatencyMon to see if you might have missed something. 
 
 

Some windows updates kill your settings, so go back and check all the optimizations etc.  I seldom connect (hardwire - any wireless is disabled to the internet) to the internet and it takes up the day when I do, since Windows wants updates, Cake wants updates, NI wants updates (and I'm running two computers).  I've found the TASCAM drivers stable and low-latency (4-5 ms on USB 3).
 
Now, figuring out their 3 page monty game for configuring the mixer is a problem, but not the drivers.
 
@

dannyjmusic
Any suggestions out there? Craig? I know you have this interface...

 
Fortunately for me but unfortunately for you, the 20x20 has been rock solid in my studio so I haven't needed to troubleshoot anything. (I also use the 4x4 in my office and 2x2 when travelling...no drama there, either.) I did need to go to the Sound control panel after the last update for the workaround, although I seldom need more than 12 simultaneous channels so this hasn't been an issue.
 
I've found that it doesn't matter whether the 20x20 is on before or after booting SONAR. All I can suggest is what's mentioned above. My main guesses would be a need to re-install the drivers after the last update, and perhaps a sharing issue with other Sound, Video, and Game Controllers.
 
Also, if you were using audio programs prior to opening SONAR, or visiting a web site that produces sound, Windows may still be "locked in" to those. I restart the computer before opening SONAR.
 

Thanks everyone...I'll give your ideas a shot:)

Did you install and do you run everything as administrator?