Calibre 3.18 64-bit on Win10 PC.
When I use Calibre to convert EPUB to EPUB with heuristic processing on default settings to get rid of extra line breaks, it appears that instead of getting rid of the line breaks, the page get split instead and I end up with A LOT of split pages, many of them just a few sentences long.
This has happened with various books and it's a nuisance.