Real-time peak problems due to sustain pedal

Hi, My real-time peak meter has started to spike and show overloads (that lead to audio pops) when I lift the sustain pedal on my Studiologic SL-880 controller. Surprisingly this happens with just the single piano track (Addictive Keys or one of the Kontakt pianos) when sustaining several notes in a relatively sparse piece. Has anyone else experienced this before, or have an idea what might be causing it?

I should note that until recently I have been able to run ~50 tracks with many plugins with no problems, so this is a rather dramatic change. Also, LatencyMon shows nothing but bright green bars after ~10 minutes of running. And my (Task Manager) CPU meters show modest load (<20%).