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So I've tested it, and the bug that un-Hyper Trained your mons is gone, so it is safe to transfer them.
THERE IS, however, a glitch in HOME where when you view their IVs, sometimes one or two of the stats won't display as Hyper Trained, even if you know they were fully Hyper Trained. When transferred to SwSh, however, it seems to correct itself and display as fully Hyper Trained in-game, so it seems to just be a HOME graphical glitch because it remembers their IVs when transferring to the game.