Hi Eicke, It could be a customer's network is mangling packets or something, though that seems least likely. More probably, if you're dealing with tiny devices, might it be that they don't have a real time clock battery? WireGuard relies on a timestamp counter always moving forward. It doesn't have to be accurate, but it just can't move backwards. So you might try syncing your OpenWRT router to some network time server of sorts before initiating a WireGuard handshake.
Jason
