In 1.12.2 version of this mod. If you find a locked chest underground, you can simply put the same type of chest next to it to create a double chest. It will make only one side locked and the other side can be open. It kind of defeats the purpose of trying to open them.

There is another mod called EpicSiegeMobs which allows mobs to dig and break blocks to get to you if they spot you. This also bypasses the locked chests being unbreakable by you. Since you can try to get a digging mob to break it open for you. Thought I let you know! This is a great mod and has a lot of potential. I am currently using this mod in a mod-pack that I've created so some of my players pointed out this exploit.

1. duplicate of #11
2. I don't see much of a problem with this. EpicSiegeMobs are supposed to destroy everything in their path and my mod only prevents players from breaking locked blocks. They can still be destroyed by explosions and such. So I wouldn't say this is a bug