sharepoint online – SPFx WebPart started giving TypeError: Cannot read property ‘Content’ of undefined

This webpart was working on a classic Publishing site. Recently, it started throwing this error message:

Error details: Error: Error initializing application. Error: TypeError: Cannot read property ‘Content’ of undefined

When I place this webpart on a modern page, it works without problems but I do not have the luxury to serve it on a modern page. Another strange thing is that it has to be on the rootweb. It does not work under sub webs anymore.(I am thinking something has changed on microsoft recently…)

I can not even debug it because it works in the local workbench and hosted workbench.

Any ideas on how to solve this? or troubleshooting tips?