As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
During Flight #3610, Nose gear would not retract after Takeoff. Red Transition light on handle and Indicator. Air Turnback to MSP. Maintenance found uplock Proximity sensor bad. Replaced Proximity switch PN 8-018-01. IAW AMM 32-60-21. Ops checks of switch and gear swings all good.