This can be frequent, there are pros and cons. I would find out what the punter would like you to do, until then carry on just no need to be frantic. I find combination of hand and mouth usually successful. After you've tried for a reasonable length of time I find many punters are happy to just cuddle. I have repeat long-term regulars who do this, they just like the contact, the sexual closeness, being naked with a woman!
Cons? Not frantic at all, but when things were going smoothly and nothing were showing he will be down in the middle, it kinda disturb the meeting structure.
also from my experience when it happens it is game over. At least I have no solution for it. But obviously they dont like that, so keep on trying to put him up, then give up for a bit and ready again when time is up soon.
And when he is up again it is kinda forced( not proper erection or weak) coz he didnt get enough time to regenerate.
Sometimes they mange to cum sometimes not, and if not there is this awkward atmosphere, even if they dont blame me.