Hmm, I think I may have been getting confused with ffdac (been using that more recently).
Yes the buffer swaps are automatic. Generally you shouldn’t do a server.log (as it’s high latency) within the callback if possible, because the buffer isn’t recycled until the callback exits - or you could just add a third buffer to cover potential latency.
That’d be my advice for an easy experiment - move to 3 buffers from 2?