App on Android Pie has issues with making HTTPS requests

Hi,
running into an issue with an existing app. When running on Android Pie, the app (and any third party library) will frequently have problems with making any HTTP/HTTPS request, it is not entirely consistent. When I first deploy the app to a device running Pie, where the app does not previously exist on the device, it will work. When I later return to the app, or re-start the app, it may hang because all HTTP/HTTPS requests in the app fails. The error that appears in the log is this: Message: failed to connect to api.xxx.yyy (port 443) from /10.0.1.106 (port 47568) after 120000ms: isConnected failed: ETIMEDOUT (Connection timed out)

If this occurs, and then I turn off WiFi, the app will work just fine over cellular data. I've confirmed in all cases that a WiFi connection exists and is working when the problem occurs.

Any ideas?

thanks,
Dennis