Wifi stops working after phone is idle for some time

Whenever my phone is idle for a certain amount of time, I don't get any notifications. So I turn my phone on, turn my wifi off then on again and everything returns to normal. Any idea what could be causing this?

Some things that might help:
Latest PureNexus
Latest EX kernel
I have amplify and greenify installed, and I followed limitations by this guide.

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