Did finish 8th in league 1 last season and relegated to one level below. Don't remember this ever happening before (and i've been around for a long time…). Any ideas why this happened?

According to the FAQ https://littlegolem.net/jsp/faq/index.jsp#tab_3

“Generally…

…players who finish 1st or 2nd in their league will advance and compete in the next highest league in the next Championship Tournament.

…players who finish 3rd, 4th, or 5th compete at the same level in the next Championship Tournament.

…players who come in 6th place or lower, will compete in next lowest league in the next Championship Tournament.”

Not sure, how it is related with the number of players in the group (which varies greatly).

@Galdian you are correct.

Everything make sense. There is nothing weird.

In general, it seems like you are relegated if you finish in the bottom HALF.