Thank you very much for the reply!
I went to make the breakpoint and it turns out I was using a script tag in the client towards an old version of pixi on Cloudflare before the addition of onLoop. I am updating the script tag to a static route towards the correct file in node_modules (per https://stackoverflow.com/questions/27464168/how-to-include-scripts-located-inside-the-node-modules-folder).
I am indeed rather new to open source and had some skittishness about digging into libraries. I'll abolish that effect - for the future, when overriding a Pixi class, do you modify the js file directly or some other method?
Thank you again.