Internet access via wi-fi is ok, but just not financial apps I have hit the same problem with a couple of apps on an Android phone. The phone has no issue with Internet access using wi-fi. Web browsing and other apps run ok. However, two apps hit connectivity issues when the phone is on wi-fi. During the moments I am facing the problem, if I turn off wi-fi so that Internet connectivity switches to cellular (4G), the apps breeze through immediately.
It so happens that both apps are finance apps. One is a bank's app and the other is a payment app. Both are not related to telcos, ie they don't use cellular for authentication. They have been working fine on wi-fi all along until recently.
What could possibly explain this behavior?
Check WiFi device if you are the owner. Some adjustable features like QoS, priority or Gaming may affect some Apps.
Then check with the provider behind the wireless service. They might have blocked some ports or IP addresses, intentionally for performance or security reasons.