Why Am I Still Having Wi-Fi Issues?

Okay, so, I've tried everything. In no specific order, I've factory reset the console, I've done a hard shutdown, I've changed WiFi names and passwords, used no password, etc. It's not that the Xbox won't connect, it doesn't even find the network! And if I try 'Test Network Connection' it gives me an error and says my hardware is messed up and I have to send it in. So I went out and bought a WiFi Card for the Xbox and replaced it myself (super easy, the case pops off and there's 2 screws holding the chip). I powered it up and BAM it works. I play a bit, watch some YouTube and then I went to bed. I get up this morning ready to play and it's doing the EXACT. SAME. THING. What could it be? The only thing I can possibly think of is my Internet source which is a mobile hotspot. But it worked last night, so I have no idea.