Not 100% answer to your question but… I am working on converting a 0.14 plugin as well. The Schema format in plugin Schema.lua has changed, there is also a legacy plugin schema conversion code, but the fact that that has TODO: 's in it doesnt make me very confident that it can handle all cases.
There’s a routine called convert_legacy_schema in plugins.lua
So that is 1 thing I know is different. Also some lua libraries that were deprecated have been removed but it’s kind of trial and error until getting something that works.
I am actually seeing a similar behavior when trying this out in K8S. Here is an issue I opened in the github tutorial I followed to add custom plugins. Did you mange to resolve your problem and if so do you mind sharing?