I deal with some of this in this old answer.

Unfortunately, the sources aren't clear and the narratives that survive are confusing. Procopius' works are more concerned with making various moralistic points than reporting history, and so his work is rather difficult to use as well.

Here's my take on it, mostly summarized from the above link:

The Shahnameh eulogizes Khusrau Anushirwan as the ruler of a golden age. But sigillographic evidence suggests that Kawas succeeded Kavadh regularly, and was then overthrown by Khusrau - thus, Kavadh probably did not favour Khusrau. If we take Khusrau's attacks on the Mazdakites as at least semi-historical, then there's a way to tease out a plausible explanation for the source discrepancies. Khusrau overthrowing Kawas and then persecuting the Mazdakites would suggest that he was actually supported by the anti-Mazdakite factions. If one wishes to paint a continuous narrative of reforms by Kavadh I and Khusrau I, as presumably Ferdausi's sources did, this is a bit troubling. Therefore, striking out Kawas and having Kavadh turn against the Mazdakites serves to harmonize the end of his reign with that of Khusrau.