In both the ALEERT and Texas House reports, it is mentioned numerous times the lack of radio reception in the building.
School PD had radios that worked in the buildings, and had to carry a second radio to communicate with the Uvalde PD. Uvalde PD radios weren't reliable inside the building.
Here you can see an officer leaving the building to use his radio. Shortly after is where dispatch tells them they've received a call from inside the room.
How did the recently conducted drills not identify the radio comms issue?