No, there is no consensus, and there probably never will be.

One thing that's important to keep in mind is that in that period, the monarchy was not in good shape. The strong Thai monarchy we know today came about in the 1960s. The two main political factions in 1946 were a left-wing civilian faction led by Pridi Bhanomyong, who was prime minister at the time of King Ananda's assassination, and a right-wing military faction led by Plaek Phibunsongkram (hereafter, Phibun). Neither particularly cared for the monarchy.

There are four main possibilities as to who killed King Ananda.

1. Pridi had him assassinated.
2. Phibun had him assassinated.
3. Bhumipol killed him by accident.
4. Bhumipol killed him intentionally.

Nobody has ever been formally accused of the crime. However, Pridi was informally accused via rumormongering. This forced his resignation and ended his political career, and set the stage for Phibun to return to power in 1947.