In the last few days LP has slowed right down when using Frescobaldi - engraving a one-bar snippet took 25 seconds! And it was completely hogging one processor - 24.9% utilisation on a 4-processor machine.
The only thing that I can think of is that inadvertently I double-clicked on the LP icon rather than the Frescobaldi one at some stage before the slowup happened, but that just produced the standard test file output.
I've tried uninstalling and re-installing LP, but that didn't change anything.