Try powering the Uno using an external power supply. Perhaps the IMU needs more current. The following is from the arduino.cc docs at Arduino Uno Rev3 | Arduino Official Store.
The Arduino Uno board can be powered via the USB connection or
with an external power supply. The power source is selected
External (non-USB) power can come either from an AC-to-DC adapter
(wall-wart) or battery. The adapter can be connected by plugging a
2.1mm center-positive plug into the board's power jack. Leads from a
battery can be inserted in the GND and Vin pin headers of the POWER
The board can operate on an external supply from 6 to 20 volts. If
supplied with less than 7V, however, the 5V pin may supply less than
five volts and the board may become unstable. If using more than 12V,
the voltage regulator may overheat and damage the board. The
recommended range is 7 to 12 volts.
By the way, I think modern genuine Arduino USB serial are CDC ACM. Clone board frequently use cheaper alternatives such as CP2104 or CH340 neither of which are usable with the USB host shield. So if you have another Uno, it should work plugged into the USB host shield using the CDC ACM driver. Some very old Arduinos uses FTDI instead.