As far as I know, chests won't produce any better loot by waiting for higher levels - there's been some discussion on these forums about this topic before, but you're welcome to try to prove it wrong.
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I don't know which discussion you mentioned, but read this :
a post of Macbeth from Larian StudiosI let you know if I'm more satisfied when I wait to open chest at a higher level
I even don't know if the loot get "fixed"(??) if I'm close to a locked chest and try open it, but my Lockpick skill isn't high enough !

(I play on Xbox)