when I sign up for a user, captcha will show me a bug Can not verify that you are not a robot. (variable K2_COULD_NOT_VERIFY_THAT_YOU_ARE_NOT_A_ROBOT). Captcha is set correctly and works in other locations OK.

joomla 3.8.13. K2 2.9 www.eshop-diochi.cz/cs/login/registrace

Captcha returns a timeout-or-duplicate error. If I think correctly, the recaptcha v2 check is online with javascript, and if the form is sent by a button, the check will re-run.
Therefore, it is not necessary to call verificationRecaptcha.
There is an error in the code. This does not allow registration with captcha.
Also, it is not good that all form fields are checked online, but only the captcha is checked after completing the form.

This error occurs to me since September 25, 2018, probably at the time, something changed in captcha or K2.

I know it and I have it correctly.
the captcha is displayed correctly, but it does not scan properly.

Registration is done in /components/com_k2/templates/register.php.
Calling the captcha scan feature is in /components/com_k2/templates/register.php
and verifyRecaptcha () is in components / com_k2 / helpers / utilities.php.
But in the verifyRecaptcha () function, there is an error, Captcha there returns the timeout-or-duplicate error.
I do not know whether I am thinking correctly, but the recaptcha v2 check is done online by javascript, and if the form is sent with a button, the check will be done again.

I had to /home/components/com_k2/helpers/utilities.php edit the verifyRecaptcha () function to always return true. Otherwise, it was not possible to register.
However, this is not a good solution.

I have returned my changes in /components/com_k2/helpers /utilities.php.

Try registering at www.eshop-diochi.cz/en/login/registrace.

There are no JS errors in the console.

captcha returns a timeout-or-duplicate error.
captcha on other sites works well

this error occurs since September 26, 2018.
It is possible that there has been some change of evaluation by google recaptcha

sorry, this is OK - www.eshop-diochi.cz/cs/login/registrace

go to setting then you can fix it

I do not understand. As?