That sounds like a very oddly specific problem, have you opened an issue in Nuxt’s Repo. My guess is they might have a better idea to why this is happening.
Have you checked this thread over? It looks like it might have some useful information to NUXT & Netlify forms users 
In the mean time, I suggest you create an issue over on Nuxt’s repo. Just in case, I’ll make sure to escalate this for you. Perhaps @luke could help
Kudos to you for finding a temp solution. Hang tight… either Nuxt or Netlify should find a proper solution soon enough.
Kyle.