DFR0535 - solar power manager trigger pin not working?

Hi - was hoping someone can help me with this board. Ive had this DFR0535 board for a few weeks now and have been working fine up until a few days ago. I run the power to all my sensors from the 5V ports and switch the whole controller on and off using the blue EN1 pin (HIGH or LOW). But now, when I switch the pin HIGH, the pin goes HIGH and the LED comes on for a split second and then goes off again. Any idea why? Ive changed everything, and still does the same thing (different Arduinos too) Pro mini, Pro Micro, NodeMCU - all of them same thing. EN1 wont stay HIGH and thus none of my sensors can switch on or off. Any help? Is the board broken? I have noticed that this only happens when my arduino is not connected to USB. While on USB, it works fine...