From your specification sheet...Frequency range: – ±10%: 1,0 to 5 000 Hz – ±3 dB: 0,7 to 10 000 Hz.
This more or less says it all. The transducer you are using has very little value at 12 RPM. The portion of the specification reading ±3 dB: 0,7 to 10 000 Hz is the key part as is the curve titled Typical Frequency Response. +3 dB is a 41% error (reading high) and -3 dB is a 30% error (reading low). At the low end, the 0.7 Hz or 42 CPM, the device could exhibit these errors. The device essentially can't detect components in the vibration signature at the typical frequencies of 1X (12 CPM) and 2X (24 CPM). These of course are commonly associated with unbalance and misalignment.
As I said, and "BECAR" reinforced, unbalance would not normally be a factor at this low speed. It would be desirable to know the actual machine details. We don't anything except it rotates at 12 RPM.
By the way, your misalignment found.pdf file doesn't open, at least for me.