Manitowoc ice machine throwing slow harvest. Checked the obvious, what am I missing?

Manitowoc Indigo, about 4 years old. Restaurant kitchen. Customer says ice production is way down — they used to harvest every 18-20 min, now it’s 35-40 min.

– Cleaned the condenser, was filthy but cleaned good now
– Water filter just changed
– Inlet water valve operating
– Sump pump pumping fine
– Refrigerant pressures look OK on paper

Harvest cycle initiates but takes forever to drop the slab. Bin not full, no ice damming.

Before I start swapping parts — what’s your gut?