In Star Trek: Discovery season 5, episode 5, “Mirrors”, Detmer and Owosekun were assigned to pilot the Mirror Universe’s ISS Enterprise to Federation HQ by Captain Michael Burnham (Sonequa Martin-Green). This explained Detmer and Owo’s absence for the rest of Discovery season 5.
However, Detmer and Owo do appear in Star Trek: Discovery’s epilogue scene, and they were a sight for sore eyes.
Yeah, I never thought it was anything deeper than that they’re working Canadian actors who probably had other projects. I looked both of them up because someone in another group I frequent was chirping about it, and Emily Coutts recently wrote and directed her own short film, and Oyin Oladejo got to play the lead in an indie thriller.