The altitude shown on screen turned wrong at 2^63m or higher and kept at -1m or 323m at 2^64m or higher.

The reason of this bug is the long long int overflows at 2^63. 2^63m is about 9,223,372,037Gm(975ly), which is considered very difficult to reach, but It actually could be easy to reach with another bug.
When the actual altitude is over 2^64m, the altitude shown on screen will keep at -1m(before load again) or 323m(after load again)