Gates close on every server restart, it doesnt matter if you have them open and disable the auto close feature, they will always close. I think regular doors remain open (most of the time) and hatches, but gates close 100% of the times.
Since this feature is broken and not reliable (even doors and hatch doors are not 100% accurate) some players remove their gates. People do that so others can walk through their bases/defences without any blockades, the idea is keep the way clear and only seal it if necessary.
Last night I was attacked and found myself unable to place my gates back, apparently the game considers placing a gate back on its frame an act of “building”. So, to help us keep our servers a healthy place help us with this problem. Either allow us to place gates back, even if we are under attack, or fix this auto close feature. I dont wanna keep my base sealed and dificult peoples passage.