Combination locks are completely useless after a server restart.
The code you set no longer works following a server restart.
Only way to remove lock is to "dismantle gate", then you can never place the lock back on that gate unless you completely rebuild the fence panel.

The biggest part of DayZ is base Building (on our servers at least).
Currently we cannot secure items in a base, as if you leave the base to actually play the game, you risk not being able to get back into your own base if the server restarts.
Server population is super low and the main reason given, is because base building is completely ruined at present.