I have replied privately, but for the interest of others, these optical compressors very occasionally fail because the transistor driver circuits can be quite stressed under very heavy continuous compression. The LEDs that make the compressor work are driven by transistors that control current from the power rails. It’s usually the PNP transistor (often a 2N3906) that fails. I hasten to add that this is by no means a common fault, but I have seen it. 😥 But most of these compressors are getting on for 20 years old now and there have been very few failures!