I used to have intermittent wifi issues with my Rpi 4b running Volumio: the device would every now and then unexpectedly disconnect from wifi and not re-connect until I did a reboot by turning it off / on. Typically it took 2 reboots to get it working. Which is, of course, very annoying as you cannot reach the Volumio UI unless you reboot.
The setup is simple: Rpi 4b, 4GB RAM, KKSB case (45C average temp), Topping E30 DAC, Samsung T5 1GB external SSD.
At some point I thought this was caused by insufficient power supply because I tried running both the Rpi and the Topping E30 on just the official Raspberry power supply. I switched to a dedicated power supply for the DAC but the disconnects were still there.
A week ago this happened again, but I wasn’t able to reconnect - no matter how many times I rebooted. I managed to get into Volumio by connecting via ethernet from a laptop, disconnect and then connect to the wifi network again. This has solved the problem for a short period of time: after some 3-4 minutes the connection was lost again.
Thinking this might be caused by a degrading SD card, a took a fresh one and flashed Volumio from scratch. During the initial setup I was not able to connect via ethernet at all (several reboots, unhooking the eth cable, etc). Since the wifi hotspot was on by default I connected to it and configured the wifi connection. The new setup worked for maybe a day without disconnecting, but then it all started again.
Frustrated, I started googling 
and came across mentions of the USB 3.0 messing with wifi in Rpi. Ok, I connected the Samsung T5 external SSD to the USB 2.0 port on the Raspberry - voila, 7 days without interruption!