I am also running a commercial 8-channel gateway at my workplace, but due to Corona I am 100km away from work in my home office where I don’t have an 8-chan GW available.
And the last time I was at work I seem to remember that the same thing happened there as well, but this was months ago and I did not (yet) pay a lot of attention to it (I was working on other problems/aspects back then).
If this is a likely cause, I can drive there next week and give it a try. But if this is just “we don’t want 1-chan GWs, go away” I might try something else instead and save the 200km drive.
But thanks for your response, I appreciate it, as it points into a direction I did not think could cause that. Always good to look at new directions! 
Helmut