2.4 GHz connections not working?

This is a weird one. So, I have the dual band XB7 router. All the devices I have that rely upon the 2.4 GHz connection cannot connect to my network (specifically: Blink Camera sync module, VTech Baby Monitor system, HP OfficeJet 8620 wireless printer). They were connecting to this router just fine up through Monday 12/9/2024. At some point that same night, we had some kind of blip. My Blink system went offline, the VTech system stopped working, even my son's Alexa speaker disconnected and wasn't playing music anymore. 

I have everything connected to WiFi now except for Blink/Baby Monitor/printer mentioned above. What is super weird is that I keep trying to connect these three devices to WiFi and they constantly say the password is incorrect even though it isn't. 

Steps I've taken to try to fix this:

1. Factory reset the XB7 router.

2. Factory reset Blink Sync Module, HP Printer, and VTech Baby Monitor.

3. Split network broadcast into two bands 2.4/5, and connect just these three devices to the 2.4 system. Same issue - password not recognized - even after changing the password to something different than the "combined" SSID password.

4. For the HP Printer, I tried doing the WiFi Protected setup via PIN. Still nothing.

I find it totally strange that my laptops, desktop, phones, tablets, Roku boxes, Alexa speakers, and Samsung Gear watch all have no issue connecting to WiFi, but these three specific items don't - and they all rely upon the 2.4 GHz connection.

Anyone have any theories? I'm stumped.