runouw.com

Super Mario 63 should seriously have bug fixez & updates! I keep finding theze nasty good-for-nothing glitches that affect coins. One involves when after a coin comez out of an enemy, & that evil glitch prevents me from collecting it! It's so unfair! Not to mention sometimez the itemz just disappear entirely! They prevent me from completing the level! I hope Runouw fixez this soon.

Unfortunately, services for SM63 are mostly discontinued. However, runouw is working on another game, Last Legacy. If you'd like to switch over to that game (which has a lesser amount of bugs) then be my guest.

I'm not 100% sure why coins become uncollectable, but I do know why the items disappear.
viewtopic.php?f=15&t=6477&start=90#p257109