Frankish vowel shifts

There a two etymologies for muse, amuse, one of which cites *muotan as the origin. If that's true, PGm. /ō/ would be rendered as /u/ in French.

But Proto-Germanic *hrōkaz (Old High German (h)ruoh) is borrowed as frox, fru, in modern French it's freux.

Do you see that as contradictory?

Well, if the same sound ends up in modern French as two different sounds, I wonder why that is. So I'd like to be able to compare other words that were borrowed from Germanic ō, to see if there is any general rule or pattern to them. And maybe through that, we can figure out whether Frankish still had ō, or whether it had already become a diphthong.