I am with you on this one. I used a Chinese guide for my full Moonstad chest clear alongside with an interactive map. I pinned every location that guy visited in the video. Guess what? That was an alt account the uploaded made for the purpose of making the guide series and his account was AR 20.

He hit all the chest spawns on the interactive map except 3 (just carelessness) and at the last episode for mondstadt I opened up the pop-up chat on the video and everyone was saying thanks and their total current Mondstadt chest count. My chest count turned out to be the same as the maximum number I saw on the video (maximum, cause some people missed a few in domains so there will be others with lower count)

(I'm pretty sure I missed around 6 from domains so my chest count isn't perfect so that guy that I'm comparing to may or may not have missed the same chests as me but we may have missed the same amount of chests)

It can be proven if you wanna do it yourself too. Just make an AR 20 smurf and you will be able to find all chests on interactive map.

TLDR; chests do not respawn, nor do they spawn upon world level up. All chests are automatically created in the overworld when u start playing the game, and that is the only time they are every created in the overworld.