I have a really simple test circuit with the AD5292-20k where the VDD, VL and terminal A are tied to the 3.3 V supply while the VSS and the terminal B are tied to the GND.
The voltage shown on the following plot is the Wiper voltage referenced to GND (nothing but the oscilloscope connected to it ), I have a really simple code on the microcontroller to increase the wiper position 1 step every 2.5ms (I have tried also increments every 100 ms with the same results).
As you can see from the waveform, the digipot works fine from position 0 (at GND) to around position 286, then the output voltage gets flat from position 287 to around position 412 where the voltage remains at 1 V. Then, at around position 456 the Wiper voltage makes a 1.1 V jump to settle at at 2.1 V and remains there up to position 656. Finally from position 656 to position 1023 the digipot behaves as expected.
I tried the 100k and 20k versions with the same results.
Any clue of what can be happening?