Xfinity wifi in low -7xdbm, intermittently cuts out several days after a gateway reboot

Hi,

One of my cable boxes has a low dbm wifi connection. If I reboot the gateway it will be good for several days and then start to cut out intermittenly.

I've tried adding an extender pod but the cable box doesn't seem to switch over to the extender, still reports a low level wifi connection. The cable box is an Xi6.

thank you

Mike