Thanks, Peter.

I've disabled the Speed-up generation option, and am running a four-bar JukeBox job on a large directory of songs. It may take several hours, but it didn't crash after three songs this time.

Perhaps you can clarify the meaning of "generation".

I have understood it to mean the process of selecting appropriate RealTracks phrases for assembly into the complete song, and that this would be done every time a song is played UNLESS the part is frozen.

This implies that, if all of the RealTracks in a song are frozen, the decision about what phrases to play has already been made, and the delay between pressing Play and the start of the song relates to the assembly of the phrases.