There's nothing specific to each map.. Does it happen a lot then?
Not really looked into the nitty gritty of how connections are handled so cannot speak for that with accuracy. There's surely a keep alive communication and it is possible that this was lost. If you force quit mir and log onto another character, you might be able to still find yourself in game while the server is deciding if you are going to reply or not.
I am sure you can extend that time but you risk being stuck in game longer if you lag out and thus more chance of death.
As you say it is unlikely to be a connection issue (on either side) since you remained connected on other characters.
I recall historic complaints that switching to a web browser like that was causing players to get kicked (some cheat prevention affecting system timings) however nothing was ever confirmed. I am not even sure if it was resolved. In any case that incident prompted us with a warning (we like to keep tabs on who tries to cheat) and there's not been anything for you..
There's loads of reasons and possibilities. Maybe Windows had a blip and the other characters had confirmed the keepalive just in time whereas your main missed it. All speculative although your situation seems odd.
As for other times, disconnections could be as simple as a router, somewhere, anywhere, between you and the server deciding to drop packets for some quirky reason. It's not that the server has suddenly decided it doesn't like you