USB Device ID customization on Raspbian jessie and up has changed.

[dernyn]

Some changes have been implemented on Raspbian image in jessie 2017 -01 and higher- that is beyond version (2016-05-10), that I believe stops USB gadget device ID customization from working properly with your startup script, the sysfs partition starts a conflicts with your device ID implementation on the startup script due to a system daemon locked file, therefore it uses the native USB gadget mode Hardware/Device ID, instead of the desired File on /sys/kernel/config/usb_gadget/poisontap/UDC which is system locked from userland.