I am having the same issues. I had to roll back to 4.7. I have a multisite. 4.8 works on all the site except one.
For the one website that doesn’t work, here are the specs:
I did recently migrate from a DEV to PROD server.
For The internal domain name, the Contact Form 7 works,
For The external domain name, which is rewritten by Access Manager (NAM), contact form 7 breaks and I get infinite spinning icon when submitting.
Development tools:
{“code”:”rest_no_route”,”message”:”No route was found matching the URL and request method”,”data”:{“status”
:404}}
Any help would greatly be appreciated.