As soon as you said SSID, I figured what it was.
I have 2 SSIDs in my house, 1 for 2.4Ghz and 1 for 5Ghz.
My phone always connects to the 5Ghz SSID, but I'd put the other one in the settings
Apologies for wasting your time.
I'll add both SSIDs in the settings field.