Do not use these ports with increments of 1.
Don't use 57555 grid 1 and 57556 grid 2.
Sometimes it works, often it won't.
For example use 57555 and 5755 for grid 1 and 57560 and 5760 for grid 2 etc.
Plus, don't forget that the seamlessdata port (27000, 27001 etc) needs to be forwarded too.
This solved al my problems with it.