Slow saving when devMode false, but not while true All of a sudden, saving entries became really slow (up to a minute). Regardless of entry type.

I came across this question: Saving entries in admin panel

Problem is when I turn on devMode saving goes without a problem and only takes a second, so I am unable to debug it.

Does anyone know why saving all of a sudden is very slow, and/or why saving is fast only with devMode true?
I cleared all caches and updated file index, and now everything runs smooth. No idea why, but it fixed the problem.