Hi, your VPS is way far more powerful than mine...
I do not want to present myself with as an expert, I'm not, but I do not understand how any command (included MaxRequests) can affect 2 different subaccunts. They are identified with different numbers. And should be treated by Oanda as totally different access.
I guess should be something different. Try to trade the same accounts from different VPS or computer for a while without any specific setting. I never had an issue like that but I am trading only one subaccount at the time. I usually connect a second Zorro to a different subAccount only for download data once every while.

I am just starting to use another broker and I have decided to use a different vps, to be on the safe side...