There is an error in test cases:
Your solution - public class MySolution {#region Solution public string Solution(string time)
gives wrong result when converts regular to military time.

Please, try this test cases:
Assert.AreEqual("0333", converter.ConvertTime("3:33 am"));

String lengths are both 4. Strings differ at index 2.
Expected: "0333"
But was: "0303"

Assert.AreEqual("NaN", converter.ConvertTime("23:33 am"));

Expected string length 3 but was 4. Strings differ at index 0.
Expected: "NaN"
But was: "1133"

I got the same error when I miscalculated previous rank.
If a user ranked 1 completes an activity ranked -1 they will receive 1 progress.