Without any multiplexers or line drivers, a Adafruit module needs 5V to connect it to a Mega board or else the level shifters don't work.
I think the BNO055 uses 13 mA maximum, the Arduino Mega can supply that current.
You did as if you would put SDA and SCL together in a twisted pair, then you did as if they are separated, each with a GND, then you have PCA9615 line drivers. You should have given the full schematic with all the used wires and distances and links to all modules in your first post.