It happens to me a lot when landing roach in the 10" class. If a sprightly one does the odd somersault in the net before I can reach it, invariably the hook dislodges and ends up hooked in the net. I'm talking of barbless 16 to 20's here and as whitty says , probably due to slack line. The next fish can be hooked fairly and squarely in the top lip fishing off bottom or the bottom lip if over depth.
It happens, but I do check my hook, particularly if the magg doesn't slip on easily..
Generally speaking, with small hook fishing it is usually the kinking of the hook bottom (1,5/2lb bs) that means a hook change, and usually when I'm catching steadily, so I accept this as par for the course. Nothing worse than a hook bottom not hanging vertically! The angle of the dangle, so to speak....
Amazingly, on the odd occasion, having caught (say) 30/40 roach the hook bottom is still in perfect nick, but rarely...