I've had a few instances where Lin disappears from the selection. Her level isn't going backwards but it still disappears after a while.
That fixed it. Speaking of the sleep options, I know the recent 0.18.0 and 0.18.1 updates change things, but we can still "Sleep with Lin" despite her "mute maid on the run" status (yes, I know the game said it would act like her event didn't happen to keep her at the hotel) but "Sleep with Felicity" and "Sleep with Felicity and Emma" are now removed even though they got a similar "to be continued" message as Lin. You can go to Felicity and Emma's door at noon Mon-Fri and click on "Visit Felicity & Emma" at college, but they aren't at college.