Temple Chain Deconstruct Issues

I am trying to get a temple chain going and I'm having issues keeping it alive. At the start of every run i do the following:

A. attempt to add to the chain if i have the right rooms.

B. Or no rooms are compatible with the last room in my chain so i place a few filler rooms in the middle (especially if they are rooms that i need but didn't appear in the right order and couldn't be added to my chain).

C. I run the temple to farm medallions. I clear every room in the temple (completed temple) then go back to the console.

D. I put a lock on the last room in my chain then click close temple.

This is the part i don't understand. The last six times in a row i have done this, the lock i place is immediately destroyed when i close the temple. I thought your last room in the chain is typically safe. I have filler rooms in the middle that can be destroyed instead.

Why is my lock immediately getting destroyed when i close the temple every single time? Do i really need to keep placing locks on my last room every run? I though your lock stays in place until you can add more rooms to the chain (then lock the new last room)?

Finding the right rooms is really hard so i would appreciate any knowledge on how to prevent this destabilization issue that happens to the end of my chain every run.

Thanks!