I will check the runtime distribution for multiple peaks representing solutions of different time complexities, however I often see the multiple peaks but find that the solutions at both peaks are the same. My guess for what is happening: the runtime of accepted solutions depends on the number of test cases. If there are new test cases, recent submissions will appear to be less time-efficient on average.
I've copied a sample submission from a distribution peak with low runtime and submitted it as my own to test this and the result had a runtime closer to a peak with higher runtime, which is consistent with my theory.
Problem #1 is solved with a O(n) solution when the problem has 10 test cases. This results in a time distribution with a peak centered around n ms.
Then months later when Problem #1 has 40 test cases, more people solve Problem #1 with O(n) solutions. The new accepted solutions result in a time distribution with a peak centered aroun 4*n ms.
Viewing the time distribution now, there would appear to be two peaks (misleading be into believing there are two "classes" of solutions wrt time complexity), however both distributions are actually the result of the same class of solution.
The percentile reported when submitting a solution may falsely indicate I have not found an optimal solution yet, so either:
Potential changes that could fix this issue, in decreasing order of how well I personally think they solve the above issues: