ADP5090 demo platform Enegery Harvesting


I'm using the ADP5090 demo platform for Energy Harvesting on my Bunch WSN nodes. It sometimes works but more often not, as the connection is very unstable. Depending how I connect the Bunch WSN to the ADP5090 board, completely entered or not, with an angle or not, it sometimes works, sometimes not. Is this issue known? What can I do to fix/stabilise this?