Trying to toggle a chest open/close state with proximity event.

I don't think I will ever be able to explain this correctly.

So I tried to make a proximity event that pretty much goes like this:
Player in proximity around the chest -> Chest plays open animation -> Chest froze in open animation -> Player left proximity around the chest -> Chest plays close animation -> Chest froze in close animation

As you can see it's kinda a toggle state with animation thrown in. However, when I try to do it, it just keeps looping the animation over and over.

I made a parallel event that keeps checking whether the player is in proximity of chest.

Parallel events loop over and over, so I suspect this is where your issue comes from. However, we cannot suggest anything without seeing your event. Please post a screenshot of the event, with the entire event window.

Have you tried Yanfly's event chase player plugin?

http://yanfly.moe/2015/10/21/yep-20-event-chase-player/

Normally I am not one for "Just use a plugin" as the first answer, but proximity to player event reactions tend to be a bit of a pain with vanilla eventing.

Without the "chase" portion of the script, you should be able to set it up to "react" via animation shift, using facing movements as a consequence of the "alert" mechanic. & then the chest would close automatically, with the "alert" mechanics expiration.

You'll need a check in your parallel process so that the open animation only plays when the chest is closed and vise versa. If the chest is already open, you don't want the animation playing again.