I've chatted with Majid yesterday to solve this problem, but unfortunately I did not receive a follow up or did not see a created ticket.
After Majid checked the issue the error message now shows at the top of the form instead of the right top of the browser screen. We were thinking it would be a plugin issue.
The B2B registration form is handled by this plugin: WooCommerce Wholesale Lead Capture
When I deactivate the plugin I get this error: https://imgur.com/a/zekst
In the security tab of the plugin configuration I saw some wrong configured Recaptcha keys so I replaced them with good ones. Unfortunately this did not solve the problem.
Thank you in advance for the support.