You could still have a look at the ContainersIgnoreOwnership setting and try out what happens if you change it. If it is ‘on’, then chests can be locked (in PVE).
I have no idea why you would want to enable locking on a PVP-Server, the setting should be ‘off’ (so ownership would not be ignored) to make it harder for your enemies to loot your chests because then they would be unable to open them because they do not own them (i.e. they are already locked to them although you do not see that on your own chests).