reCaptcha broken

We are using gravity forms. Some of the gravity forms with recaptcha, we get the error “The recaptcha was invalid. Go back and try it again”

Why does some of the forms say this and others do not?

replicate:
use gravity forms latest version
configure recaptcha

check the reacaptcha on the webpage, and hit submit
“There was a problem with your submission. Errors have been highlighted below”

I am using w3tc cache plugin too.. Have anyone here any ideas for troubleshooting this? Some pages work and others do not. I don’t see any obvious errors in google dev chrome tools

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