I'm glad I found this conversation. I was having the same problem when I was transferring an app from VS 2019 community to codepen.io. It worked fine with React and node.js and using MS Edge. But, on codepen.io, I was getting an error in the Chrome console, Type Error: Cannot create property '_gsTweenID' on string '#el' followed by an infinite loop error Uncaught Type Error: Cannot read property 'length' of undefined.
After reading this conversation, I solved my issued by creating a jQuery-like function (sorry, I'm still new to coding and haven't delved into jQuery yet):
function $(x) { return document.getElementById(x); };
and then changed all of my tween targets from :
.to('#el',SPD,{animation:object})
to:
.to($('el'),SPD,{animation:object})
The app works like it should now.
Thanks again everyone!