I should have specified countries I guess. Austria, Germany and Netherlands for sure. Others I'm told but have not directly experienced it.
I get that from working with and for German, Austrian and Dutch companies in Germany, Austria and the Netherlands. It's nigh on impossible to get anything done in August around here.
This doesn't apply to things like resorts and restaurants, for obvious reasons, though if that's what you're thinking of.
I found one Austrian source ( https://www.vol.at/wo-die-produktion-urlaub-macht/3314076 ) mentioning the issue and I can see how it would make sense for some industries to need some maintenance time each year.