More than likely the rotary valve is to blame. The rotary valve “When not working correctly” can pickup from one station and dump into another. This can happen if the rotary valve o-rings or sealing internal is not to manufacturer specs. It can also happen if after it picked fluid from one station and then the rotary valve advanced a few steps and returned fluid into incorrect station "Bottle"
It is true this particular processor is a "Work Horse"
I'm betting you had one bottle low on fluid or empty and another full?
Usually the bottles “stations” are next to each other.
Anyway this can be caused by many issues, here are a few.
1. The position sensor on the rotary valve is faulty.
2. The rotary valve seals are compromised.
3. A protocol can become corrupt.
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