I'm glad to hear you got WiFi working. I guess I wasn't crazy to suspect the BNO080 might be the culprit.
PaulCollett:
If both operations require the same pins then that's going to be problematic.
Not necessarily so. The I2C bus is designed to support many devices all connected to the same 2 pins. The I2C bus on your MKR WiFi 1010 is already being shared between the ATECC508 crypto chip and the BQ24195L battery charge controller chip. Each I2C has an address, which is used to determine which device the the microcontroller is communicating with over the I2C bus. So as long as each device has a unique address you can have many devices on the bus. This does require that all the devices are playing nicely with each other.
If you can't get it working on the existing I2C interface, a workaround could be to create a separate I2C interface on your MKR WiFi 1010 dedicated to the BNO080, then leave the existing one for the use of the crypto chip and battery charge controller. You can find a tutorial for how to do this here:
https://www.arduino.cc/en/Tutorial/SamdSercom