I remember having been bitten by this in Plone 5.1 and 5.2 sites.
Don't think this is related to plone.app.z3cform but how the base path is configured in your widget. From looking at my crappy code, finding the wrong root folder is not limited to TTW XML fields.
Will take a walk down memory lane and see what I can find. I am pretty sure some of my posts from 2020/21 are about this or very similar (will add links if I can find).
