One thing Garmin mentioned that could break the altimeter was wearing it in a hot tub or pressing the buttons a lot underwater.
A swim watch that breaks in water. Brilliant.
My altimeter never worked. I bought it right before IM Boulder last year and it had some outrageous elevation totals. Even runs with almost no elevation change will show thousands of feet. As long as it isn’t used to calculate workload, VO2 max, etc, then it doesn’t bother me that much.