☒ what issues with wicked_pdf are you having? Webpacker doesn't really have a part in it as far as I know. Are you trying to serve image assets or something via Webpacker instead of the asset pipeline in the PDFs?
I started to look at this and I think I was able to replicate the issue, but haven't seen where it affected anything negatively. I even combined a few situations where doing form field highlighting errors did appropriately flag the correct fields which failed validations.