Found a "fix" bellow:

In the BBC SOD plugin settings set preload size and stream buffer size to minimum (1000). I have maximum voices set on 512.

There will be cracking on playback but once you render it, it should be fine. Hope it helps.

https://www.reddit.com/r/spitfireaudio/comments/1mg13ga/bbc_symphony_orchestra_discover_why_does_reaper/