This is due to fact that the currently listed seasons doesn't start at episode 1.

This will be fix at a later date (not yet defined) when all the seasons will be merged in one single season to meet the original Japanese broadcast.

We can't do anything in the mean time.

The most recent few seasons also don't start with episode 1, but they have original air dates. Is it just broken anyway?

You will have to wait until the seasons are merged.

I'm cool with merging the seasons as long as all the episodes are there and in a proper order, but I am curious on a few aspects on how it would work.

1. How would this affect tracking apps such as Trakt? Will the data for the episodes remain and transfer user's watched episodes or will users have to re-mark all of the episodes?
2. If One Piece moves out of Wano Country before this happens, will a new season be made for the next arc until the merging happens?