I also use flip and DNF more than standard cubes. Here are the four main reasons I DNF-
- Small mistakes where I do the wrong move by like 1 tick, which if I don't notice messes up the whole solve.
- Doing the turn with wrong pin order. I usually notice this and it just slows me down a lot, but sometimes I DNF.
- At the end, if I miss by 1 tick, this is roughly the same level as a +2 but in Clock it counts as a DNF.
- Whenever I make a mistake, it is harder to see and notice as it's easier to notice bright colours that don't match rather than 2 small clocks that are 1 o'clock apart. Also sometimes the mistake is on the back so you can't see it at all.
While no-flip would obviously have a lower success rate, flip is still easy to DNF purely because of the nature of the event.