Onoff Shim with Hifiberry AMP

Hi There, i bought myself the Pimoroni onoffshim in order to use it together with my Pi3B and the Hifiberry AMP HAT (including an additional power supply for the amplifier). Unfortunately the onoffshim doesn’t work properly. it shuts down correctly but it is not restarting until i cut the HAT’s additional power supply and then pressing the button again. But without the additional power supply the amplifier doesn’t work. Any ideas how i get this working? Thank you in advance!