FirstNet absolutely went down in my locality (western Ohio, near Dayton). I was on shift for after hours support of a public safety answering point (AKA a 911 center) and I received a call at 04:14 Eastern stating that all the law enforcement/fire mobile units on FirstNet disconnected from the VPN and that no FirstNet cell phones could make/receive calls or send/receive text messages.

It can (FirstNet's lower 700mhz spectrum), but AT&T uses the same backbone and infrastructure and towers for large chunks of their and FirstNet's network.

(charitably) - FirstNet is mostly now just a type of billing plan and priority level, on AT&T's network.