Wi-Fi only occasionally working

Hi there. 

I have a iPhone 7 with IOS 15.3.1

My IPhone seems to loose the Wi-Fi connection after a while and not be able to find it (or any other Wi-Fi) again until you turn phone off and back on again. 

Generally if I turn the phone off then on again the Wi-Fi settings will turn on and find all the signals around and connect. It can stay working for a day or two if you don’t leave the Wi-Fi range of your router.

However if you leave the range then it often (but not always) looses the ability to see Wi-Fi signals even though it says it’s turned on. If you try and turn the Wi-Fi off (on the phone) it turns itself back on straight away and still doesn’t work. 

If you turn the Wi-Fi off after turning the phone on and wait a few hours then try and turn it on again it turns itself off straight away too. 

I have reset the Network settings and that didn’t work. I then tried doing a back up and factory reset and that didn’t work either. 

I’m thinking this is a software issue and am worried that if I have to buy a new phone (last resort) that the problem might transfer. Any advice or ideas would be appreciated.