Maybe I've missed a step somewhere? Or maybe something needs to be added to the embeded code.? This is where the form is located https://www.esabna.com/us/en/dmx/index.cfm
I just submitted that form successfully with the invisible reCAPTCHA. No image challenge appeared.
If you're able to consistently recreate the behavior, can you describe your browsing environment? Are you using Chrome? Chrome Incognito? Are you browsing via a VPN?
Additionally, what is your Hub ID? I can test the form some more on my end.