@lobosdoc.....I have the same esoteric issue with my Brother!!!
I have tried everything you mentioned and more. Brother support is useless, though the printer is still in warranty. I have a setup very similar to yours I think. My guess on what's going on:
(I moved house in between, so not sure either on some variables, like changing printer and router locations at the new house.)
Suspects:
- FW update to the printer. I did not notice issues at my old house, but maybe they were already there.
- FW update to AC68, 56, and R7000. 384.6 and 384.7. Perhaps some incompatibility on the new versions vs. 380
ONLY solution workaround that is working for me right now:
I have an 'eternal' ping from one of the routers to the printer on an init script. Try it. Even if you see no response from the printer, at some point it starts responding and then it is permanently reachable from everywhere.
So far, problem solved, but....not sure about the root cause of the problem and do not like not to be certain that the issue could not recur or go worse.
I have moved since end of July, so have only noticed the problem recently. I was pushing Brother's useless customer support....but stopped because I am not sure this is a printer issue or just a combination with the Merlin 384.X at the moment. Is your printer new?
I would also love to hear of any other ideas or alternatives, and hope the ping workaround does it for you. Let me know.