Nope, it was a bug. Hint said to spy on Sara in the bathroom in the AM and she wasn't there for what I believe was meant to be her 4th spying event. Would select the spycam from the inventory as before, but then clicking on the bathroom door would just move the MC into the space.
The error persisted for several consecutive in-game days until I got the bug of not being able to sleep at night and advance to the next day. So I ultimately started the game over from the beginning and just focused on the sisters' paths. I was able to complete Sara's story all the way* and progressed further in Caroline's story than I had been on the previous save with the phantom bathroom issue before calling it a night.
* The continuing night events w Sara seem bugged. When Sara answers the call and enters MC bedroom at night, there's s rollback error (use that what it's called?), and after ignoring it the action menu pops up. Each new event shows a new 'pussy' option, but no matter which of them I select it just repeats the stare-at-her-butt-and-jerk-off action. So I can choose from like 5 'pussy' options but none of them yield pussy. Which, I'm sure you'll agree, is a damn shame. (Note: The very first play of the night call w Sara that unlocked a pussy option played normally. No rollback, banged Sara's "teen pussy" (per the dialog) and has much fun.)