Hi,
Thanks for posting in Q&A platform.
It seems your issue is that slow Wi-Fi network connection performance when VPN is connected. For network speed slow performance issue, it's necessary to analyze performance log and network traffic to find the cause. However, analysis of log is beyond our forum support level and due to forum security policy, we have no such channel to collect user log information. So, we recommend you open a case with MS Professional tech support service, they will help you open a phone or email case to Microsoft, so that you would get a technical support on a one-to-one basis while ensuring private information.
Here is the link, you could find phone number of your region accordingly from the link below::
https://support.microsoft.com/en-us/gp/customer-service-phone-numbers
Best Regards,
Sunny
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