I don't have as much visibility into Oman, but wonder if this is part of a larger crackdown on perceived security liabilities after the ISIS Muscat Muharram attacks. There's little that I can see on the Yemen side driving this.
EXCLUSIVE: Over the last several weeks, Oman has expelled nearly all of the Yemeni veterans of Guantanamo it agreed to resettle nearly a decade ago. In Yemen they face real persecution/death risks. Some of them say they were told the US gave Oman a “green light” for the expulsion.
After less than a decade out of the infamous wartime prison, at least 24 Yemeni men have learned they weren't "resettled," after all. Part 1 of a 2-part series
Would be interested to see where they're dumping them. Got that one reportedly detained by the Houthis, but they're in all likelihood dumping them in GoY-controlled Mahrah. US has some leverage there if it cared to use it at all.