This is a known bug. Some locks don't save on server restarts. You can place blocks over the chests or get the interact deny flag so non town members can't open them but idk what else you can do :(((

 

We are working to resolve this issue as fast as possible. For now I would recommend not keeping anything too valuable in any chest locked recently and out in the open. Placing a block over the chest when you leave would be useful because then a user would have to commit (minor) grief to get to your stuff and we would be able to take some action.

 

If there is an issue with locks, I would also consider any valuables being stored in an Ender Chest. No need to worry about locks or grief that way.

Just remember to take them out if you plan to go inactive.

 

We are still trying to pinpoint the exact issue. We know what's causing it, just now how to fix it yet.