In 3.0 when the banlist table had many rows the pages which displays the banlist was still generated very fast.
However in 3.1 the pages are generated very very slow.
For example:
3.0 - 24219 rows

Page generated in 1.2381 seconds with 4 queries + 2 queries returning data from cache

Time spent on mysqli queries: 0.19001s | Time spent on PHP: 1.04806s

3.1 - 5770 rows

Page generated in 11.0586 seconds with 5 queries + 1 query returning data from cache

Time spent on mysqli queries: 0.076s | Time spent on PHP: 10.98263s

Although the 3.1 board has way less rows it tooks about 10x longer.

Originally mentioned here: https://www.phpbb.de/community/viewtopic.php?f=33&t=231868 (german)