It might be difficult to diagnose when you don't know the variety (Mirabelle?). Could be lack of pollination, or just some strange variety that doesn't readily fruit. I don't think that it would be frosts as it looks like the tree is sheltered.

perhaps the blossom finished and the petals blew off in any of the windy weather we have had. Is there any sign of the flower stalks left? a close up of where the flowers were would help.

welcome to GoY too :o)

As its relatively newly planted it has probably dropped its flowers without setting fruit. It will be using all its energy to improve its root system. Stone fruit flowers flowers don't last all that long- how long was it in flower?