Is that the bit that got added to deal with auto-processing the vendor prefixes?
In reply to Richard Oelmann
Re: Purge Cache takes Forever with Boost and Child themes
by Urs Hunkler -
Yep, Damyon wrote so in the tracker »Time to reset caches (compile Boost) recently became 3x slower« https://tracker.moodle.org/browse/MDL-58646.