With the new XL version, I can only occasionally update the the values on the fly. Most often not. The added tools are nice to have though. My system always fails to read the injected strap ... pops and error dialog box to that effect.
I still regret moving to Win10 1903 as I think that's what took away my ability to modify things real-time, while Claymore is running.
You probably need an option or button to revert out of test mode. Obviously, you can flip into test mode if you don't detect it running but then there's no automated way back out in the XL Win tool.
Edit:
bcdedit /set TESTSIGNING OFF
just in case someone was looking for it.
I've tried to recreate your problem with the straps not injecting ..
Just to be clear here, you can only inject a strap at the selected frequency.
So if you're currently running your memory at 1900 Mh and you do a modification/strap injection for freq 2000, you're not going to notice any differences.
However, that doesn't mean that you should get those error messages.
It's the driver that fails to inject the strap.
Probably something to do with Claymore's driver
Button to turn test mode off has been added to latest release
As well as NAVI10 support 
Only Strap injection and Power Play support (read from vbios/registry and write to registry for now)
Latest versionCheers!
Thanks. I'm on Claymore 11.9 so I'm not using his newer strap injection version. I'm only trying to mess with the REF at this point, but other timing regs also refuse to update. I'll d/l the latest and keep at it ... see if I can find the common thread.