Gaming Switch can't join ad-hoc games

[gygelly]

So, I've got 3 switches. All are running sx-pro emunand, and I set all 3 of them up exactly the same, for me and my daughters to share.
2 of the switches work perfectly.
But the 3rd switch can't join ad-hoc games hosted by the other 2. The weird thing is, those switches can join if the 3rd hosts.

This is true across all ad-hoc games. I've confirmed using mario-kart, dragon quest builders 2, smash bros, and stardew valley.
This issue doesn't exist if using lan mode, only the ad-hoc local wireless mode.

But if we want to play together, the 3rd switch has to host..it can NOT join games hosted by either of the other switches.
This has recently become a problem with game like dragon quest builders 2 and animal crossing, where it matters who is hosting due to the state of the world.

Has anyone ever encountered this problem, or can recommend a fix?
I'm pretty good with using custom firmware tools, etc...is there anything at least that could help me debug this issue? Perhaps a way to read logs from games? When it fails, mariokart 8 for example just says "communication error", nothing useful.