Part 107 UAS pilot reported a malfunction with the transmitter. During the post flight the reporter learned they may have flown over 400 ft. AGL.

Narrative

Searching for a lost dog at the request of a local animal rescue organization. The handheld controller changed to an unknown language (and possibly from feet to meters). There was also some confusion on my part about a setting to (apparently) limit altitude based on contour map data I had downloaded to the controller via 5G hotspot. I thought I had set the correct fields to the correct values and flew several flights intended to be under 400 ft. AGL.Later; upon uploading recorded flight data to an online logbook service; I saw unexpectedly high peak altitudes (e.g.; 429.8 ft.; 522.3 ft.). I had launched from low terrain and then flew over much higher terrain; so quite possibly no exceed of 400 ft. AGL occurred; but I intend to reproduce the controller language/units change indoors to determine how it occurred and prevent a recurrence. I also noted that working in total darkness (other than the light from the controller's screen after being somewhat blinded by the aircraft's dual and very bright anti-collision strobes) and under the pressure of trying to save a pet's life is difficult and requires much additional care.Note- I would have filed this report a few days sooner but I only recently examined the flight log reports.