my land line keeps dropping the call in one direction after a while

The call on my cordless phone will sometimes drop the connection in the receive direction to my phone after a while (many minutes). I could no longer hear the person on the other end but they could still hear me.

I can use my iphone for calls thru the Xfinity WiFi internet and that does not have any issues.

I have reset the Xfinity modem but that did not resolve the issue.

I connected the cordless phone base directly to the modem (bypass the house wiring) but that did not resolve the issue.

I bought a new cordless phone system (different vendor) and that did not resolve the issue.

Has anyone else seen this issue?

Any comments on how to resolve this issue?

To me, it seems the issue is with the Xfinity modem box and I would need a new one.

thanks,

Dan