What determines which comments are displayed initially?

Question

There are times when some questions or answers have many comments. In such cases, there's a "show n more comments" link. On clicking the link, I find, quite often, that the comments that were not shown initially, are often not comments chronologically later than the last previously visible comment but maybe even be between any of the previously visible comments. In which case, I need to go back to the top of the list of comments and work my way down to read the now visible comments.

Why is that?

Answer 1

Can't find a detailed explanation post to link right now, except for Shog9's answer to "Why are comments hidden by popularity and not by chronology?" maybe, but it has to do with the comment vote score.

Priority to be shown among the initially visible set of comments is determined

1. primarily by the number of upvotes a comment has (higher score = higher priority) and
2. secondarily as a tie break by age (older = higher priority).

The reason is to rather show comments which were perceived as useful over potentially more irrelevant comments that might have come earlier or later in chronological order.