2.4 vs 5 Ghz

I have a garage door opener that only seems to connect to the 2.4 network. 

I have a printer that only connects to the 5G network.

I have a smart plug which is very confused by all this.

The router is supposed to figure out which network to use, but doesn't seem to work great.

Is it possible the router isn't functioning properly?

When I separate the networks, I can get the garage door opener MyQ app to work.

When I try to recombine them, it tells me my signal isn't strong enough. 

The MyQ needs to be connected to my phone, which is connected to the 5G to work.

What is the disadvantage of taking the entire thing back to 2.4 and calling it a day?

Very frustrating since before I "upgraded" to the newest router, everything worked.