And, it's still not in the right forum, as this belongs in the forum for fishing & Treasure hunting - but I'll answer this for you.
There appears to be some variation of the difficulty of chests, even at the top level (paragon chests with level 5 or 6 maps) where the chest requires the GM lockpicking.
I've not seen it in dug chests from maps, but while most paragon chests take 1-10 attempts, I've seen a few take over 100 attempts, breaking 30-60 picks in the process to open just that one chest! I run into these about once every 50 or 100 paragon chests (I think the only time I ever had to pick two of these in the same day, was when a friend filled his mostly-empty 18x18 with chests before asking me to pick them all in one session - I broke more than 200 picks over about 60 chests - with around half the picks lost broken on just two of the chests).
