I just passed all checks with the same exact code twice in row and then failed one of the random tests on the next try to then complete all of them again after.

I also checked other people's solutions and they did the exact same thing.

Manual calculating again confirms that the random tests gives back a expected value that is 1 too high for the actual solution.

Yes, there is probably something wrong with the random tests.

Is there something wrong with the random test cases? Because it seems VERY inconsistent.
One run I get them right, the next run with the same code they are one off. If I do the calculation manually for those runs your expected answer seems 1 too high every single time.

My code runs fast enough to not be an issue, and it doesnt overflow anywhere so Im not sure what's going on.