Unfortunately, I am unable to tell you why this happens. All we know about the sticking if eggs at the ceiling of the cave amounts to waht Walter Foersch had found out more than 35 years ago. That it is a matter of a too high mineral content, especially calcium in the water.
It would help if we knew about other species in your water. Have you made the same observations with the eggs of them or not? Personally, I do not think it to be matter of the age of the male, since we had older males (of other species) with normally sticking eggs. But it maybe an individual problem of that male, of course.
The other thing is that I had some success with reducing the pH below 4.0, even to 3.5 in some cases. This may help, but it’s not sure, of course.
Anyway, you should try to raise at least a part of the clutch artificially. I think of the fact that the main breeder of phoenicurus during the first years, Martin Fischer, had strange difficulties himself with the last clutches. The only thing I can say is that we must try not to loose the species altogether. So, it would be good news that the development of the larvae is going on.