It's the 'X/Y' Reverb. The 'Echo Density' is on '2' on the 'X' state (Large Spring), and '8' on the 'Y' state (Small Chamber). It causing the CPU to max out, crackle, and disable the Reverb block. You can lower the 'Echo Density' in the 'Y' state to '2'. Or, use 'Normal' quality and an 'Echo Density' of '8'