Impossible to sync more than 4 devices

I made 8 light bars for our band.
Each one has 120 leds and an own ESP32.
I wanted to have 1 master and the 7 other should be synced to him.
The problem is, only 3 of the other devices can connect to the master network.
The other 4 wont connect and create their own network.
Did i miss something, is there a limit of devices in one network?

Do they just not sync are are you saying they won’t all connect to the WiFi?

If WiFi, then there’s an issue with your WiFi router/network.

They wont connect to the wifi that the 1st (master) is creating.
I forgot to mention, when more than 4 are switched on, (1 master 3 “slave”)
even a smartphone or laptop cant connect to the master.

The way sync’ing works is that they all need to be on the same WiFi network and then they can pass various protocols you specify to sync. They won’t connect to builtin AP of a single board.

I know I can connect at least one to another’s AP.

Why not just buy a cheap router and use that to create/manage the network? You don’t have to have it connected to the internet. Just use it local.