Contact Form 7 not working

I’m getting similar issues across 2 different websites on 2 different hosts. Based on my testing so far, it seems like the forms may be sending, but CF7 is not properly displaying the output message indicating whether or not it’s sent.

I’ve ruled out other plugins as a likely cause. this issue may have started after the update I installed on both sites where this is an issue on Aug 10. So it’s probably a bug introduced in that update.