Rotary encoder stops working after restart

Hi,
I’m using the rotary encoder plugin, installed through the plugins menu. When I set everything up, the encoder works perfectly, but after I restart volumio, it stops working. If I open the rotary encoder plugin menu and just hit the save button it will start working again.

I’m using Volumio version 2.834 and Rotary Plugin version 1.2.2, on a Raspberry Pi 3 Model B.

I’m using GPIO 27 for CLK and GPIO 22 for DT on the rotary encoder.
I’m also using the Official 7" Raspberry Pi touchscreen display and a pHAT DAC.
The pHAT DAC uses GPIO 18,19 and 21, so I don’t think it’s an I/O conflict.

The encoder is a Spectrol DE2-0-1-32 ( http://www.farnell.com/datasheets/319882.pdf )
I have the input (Vs) pin connected to 3V3 (pin 1) and the common pin connected to GND (pin 9). The output signals are clean and the encoder has built-in CMOS debouncing.

Any suggestions as to why the encoder stops working after a restart?

Thanks in advance!
Stu