The easiest way for us to debug this kind of issue is to get a link to the website where the issue lies. This sounds like a javascript error or conflict with another plugin. If you’re not comfortable providing the website there are some things to help narrow down the issue.
# Install the WordPress Health Check Plugin.
This will allow you to safely disable plugins for just your user. Enter troubleshooting mode, enable Contact Form 7 and Contact Form 7 – reCaptcha v2. Head to the front-end of your website and test the form submission to see if the issue persists. If it does not then you can enable plugins one by one until you find the plugin which causes the issue. You may also need to enable your theme as it could be a theme issue.
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We could also use the Operating System and Browser + Browser version. You may also use the tool linked below – we just need the last line “Browser”:
IQComputing Browser Info