It has been intermittent for me. Even when most of my pistons failed to load, a few still went through. Try the same piston again a minute later and it no longer works or vice-versa. Platform issues seem to rarely have a 100% failure rate.
This is also a good time to test your Smart Home Monitor… smoke detectors, leaks, etc. I am still getting incident reports, but please test these devices if you can. It would be helpful for ST to know whether SHM is directly affected.
@Mckenph @lflorack @smartie @Alwas @Terminal @Ervin @kevinsunny, SmartThings has completed rollout of a potential fix for this. If you were heavily impacted please give it a try to see whether the issue is resolved. It was too intermittent for me to know for sure.
If you have applied the code patch, please revert to the last published version once the fix is confirmed.
Other SmartThings users noticed problems with Smart Home Monitor which uses the same integration that was causing the 401 errors. Please read the following and check your device statuses; it seems that incidents may not have been reported reliably over the past few days.
Fortunately for me, I don’t use SHM as I have a totally separate, monitored security system.
I can confirm that issue is gone for me. I’m able to open/edit pistons via web and also via SmartThings Classic app.
Thank you very much 
I can say without a doubt that they may have fixed it. 
Last time I tried, earlier today, every time I switched from my Hubitat instance to ST I would get an error message and the ST instance would not open. I would have to try again. Usually the ST instance would open on the second try.
It just now switched back and forth several times and it never gave me an error. I also opened several pistons with no error, but last night and earlier this morning it was working fine so I will have to see how it goes over the next couple of days…
thanks for that, uk here and I was suffering the reported issues. the patch from your post rectified things for me, ta.
Glad to hear, but you should be able to revert back to the published code now since ST fixed the root problem.