fishing rod had unbreaking 3, mending, luck of the sea 3, lure 2 and curse of vanishing. I was wearing unenchanted iron armour only on singleplayer. I left my computer as my player was afk fishing (with an auto clicker) for about twenty minutes and came back before finding the rod gone without a trace. this also happened with an unenchanted rod after leaving it for about 5 mins before but I assumed it was because of durability.
Probably still be due to durability. If enough of your casts are not catching anything then you’ll wear out the rod faster than you can mend it.
Since this was an ark situation and therefore no one knows for sure what happened, it isn’t something we are going to be able to reproduce and confirm as a bug.