Newbie : Dumb WiFi Question

I apologise up front for my ignorance but I have searched without success.
My question relates to wifi coverage.
I’ve installed HA on a Raspberry Pi 3B. It in turn, is connected via ethernet to my ASUS wifi router. Alongside I have a Hue Hub.
I’ve got several devices working with HA such a hue bulbs, tradfri bulbs, sonoff switches, tplink switches, zigbee switches Etc.
I’m currently having wifi dropout problems with one or two of the tplink switches which seemed pretty reliable before I controlled them via HA (using the KASA app via my router and via china).
I’m considering why it is that i’m losing connectivity when previously all seemed fine.
Can somebody explain/confirm whether my tplink switches are talking to my strong wifi router or is it possible that they are talking to the inbuilt wifi on the Raspberry Pi?
Would a wifi extender help with this issue? Would I be better off replacing the tplink switch with a string of zigbee switches (meshed) to get to the device I’m having problems with?
Many thanks for your opinions.

If your RbPi is connected with Ethernet, the tplink switches can’t connect to the WiFi of the RbPi, since that is not configured. The tp link switches are notorious for dropping of the network regularly. Search the forum.