I experienced the same issue (intermittently) on my FP5 after updating to e/os 3.5-a15. I’m now on e/os 3.6-a15 and the problem persists.
I found some threads with a similar issue:
Someone in the first thread suggests this being an issue with WPA2/3 mixed mode or 2,4/5Ghz bands. For me it appears to be an issue with WPA2/3. Here’s what I did:
- I checked the security setting of my wifi network on my router. It is set to WPA-2-WPA-3-Personal.
- On my phone I navigated to “Network and Internet“ > “Internet“ and clicked on “+ Add network“ (below the lists of networks).
- I manually entered the SSID, and selected “WPA3-Personal“ as security option.
- I entered the Wifi password and saved.
After saving it connected immediately. Restarted my phone once, and it also connected immediately. After disable/enable wifi it also still connects. So, at the moment this seems to have solved my issue. Fingers crossed it will keep working. Hopefully it will help someone else too.