jremington:
The I2C connections absolutely require pullup resistors, typically 4.7K to 3.3V only.If the Wemos D1 mini is a 5V system (I'm not familiar with it), there will be a problem.
I think it's a 3.3V system, but it's ok with receiving a 5V current (through usb).
I'v tried connecting gy.VCC <-> d1.3V3 (instead of gy.VCC <-> d1.5V) but it doesn't change the output of i2c.scan()...