There may have been additional delays and hold ups for the Horus Heresy. I know going to print and getting the books out always takes a awhile so its hard to think that there was an additional phase in playtesting this late in the game, but at the same time this source has been rock solid for quite some time.
via a solid source here on Faeit 212
Horus Heresy is in the final playtesting phase. There was a additional
playtesting phase by the covid caused delay.
Release is now planned for June.
