@Ismael You might want to re-think the usage of Google Recaptcha (and also Google Maps).
Most likely this violates european data protections laws (see the Schrems II landmark ruling).
I assume the contact form is submitted by a PHP script? Isn’t there any chance to check if your own captcha has been filled in correctly?
You might also consider the usage of some invisible honeypot textfield. See https://dev.to/felipperegazio/how-to-create-a-simple-honeypot-to-protect-your-web-forms-from-spammers–25n8
I know IE 9 is not the most modern browser, but it still has a significant market share, espacially in corporate Windows networks. Therefore it’s still relevant for B2B websites.
So if you (or anybody else) have any idea what might be the issue (it seems like something changed between 3.4.2 and 3.4.7 I would really appreciate it. :)