I also had this issue, but I figured it out.
What I did wrong was accidentally enabling recaptcha twice on the page.
I have installed the Invisible Recaptcha plugin.
In the contact form I added a [recaptcha] block.
But then I also went into Settings -> Invisible Recaptcha and enabled the setting “Enable Protection for Contact Form 7”.
It looks like this enabled it twice, and they were tripping up on each other.
I removed the [recaptcha] block and it started working, and the recaptcha is still working.
