Wow congrats
My highest is also 54 lol you might beat it soon
This issue has been going on for a few months (at least) and still isn't fixed.
You might want to check these ongoing threads about it :
https://www.chess.com/forum/view/help-support/puzzle-rush-high-score-not-updating
https://www.chess.com/forum/view/help-support/puzzle-rush-survival-record
In short, at the moment there is a bug (some people say it isn't a bug, and might be intentional) that limits the PB display, as well as its display on leaderboard, to attemps that are 49 and lower, for untitled players.
Anything 50 and above won't show in your profile's personal best or on the puzzle leaderboards. However, those 50+ attempts will still show when you hover over your usename.
Titled players don't seem to have the limitation.
So my past puzzle rush survival highscore was 42, yesterday i beat it with 54.
But on my profile it still said 42. Today i got 43 and it changed the 42 to 43 on my profile but not the 54 i got yesterday.
Is this a bug?