Continuity mistake: Lt. Malloy has his lower left leg amputated in Isaac's attempt at practical humor. When they later find the leg, it's not just a lower left leg, but an entire left leg (upper + lower). So either Malloy regrew half a leg in the course of a single night, or they forgot to tell the prop department to only make a lower leg. (00:26:35 - 00:30:20)
Continuity mistake: The remote control device installed into the Orville's circuits is shown several times through the episode. When Isaac is beginning to send his leads into the device the corners of the right end of the device are about 1/2" - 1" past the intersection of various block shaped components of the Orville's circuits. However, just moments prior, when the device is shown in place in the same circuit, the corners of the right end of the device line up perfectly with the corners of those same block shaped circuit components as evident by the slivers of light shining between the very thin slit formed where the two sets of corners align. (00:34:15)
Continuity mistake: When the crew is working to disable the device helping Pria to hijack the Orville, the Chief drills a hole and creates a great deal of metal/material shavings on the top of the device, which disappear. The device is also aligned differently in respect to the components of the Orville's circuits from the Chief's drilling shot to Isaac's probing shot. (00:34:21)
Answer: No official reason has been given. Halston Sage has only stated in an interview that leaving the show was not her choice. It is considered that her possible return is "open ended", and while there has been no official announcement, she did make a reappearance at the end of Season 2.
raywest ★