Never even all my years of CVH ownership have I had a nut back off. Stud pull out the head, yes, but nut, nah. And I've had N/A CVHs doing ~8k rpm on the regular.
If they used the proper nut, its essentially self locking - forgotten the proper name for them but they are slightly oval'd (can see it in the right hand nut)




Hydraulic cams work harden with the rockers, so switching it for new is a complete gamble. Worst case the cam or new rocker start breaking up then you end up with an engine full of metal swarf.

I'd be asking whoever built it to be providing a new cam and lifters if it were me