A data point, since this is otherwise hard to calibrate against.
I had a submission sit at Waiting for Review for 15 days. Apple's norm is around 24 hours, so it felt exactly as wrong as yours does. When a reviewer finally opened it, they spent nine minutes in the app and approved it the same day.
Those nine minutes are the useful part. The delay was queue position, not scrutiny - nobody was deliberating, nobody had concerns, nobody had looked. That does not shorten your wait, but it does mean a long Waiting for Review is not in itself evidence of a problem with your build.
Two things worth checking while you wait, both read-only:
GET /v1/appStoreVersions/{id}/appStoreReviewDetail returns the demo account credentials Apple actually holds for your submission. If review notes were edited at any point, what Apple has may not be what you think you sent. It is a five minute check that rules out one real cause of a stalled review instead of speculating about it.
GET /v1/reviewSubmissions?filter[app]={appId} is the authoritative state. You have already established it is WAITING_FOR_REVIEW, but it is worth watching directly rather than through the Connect UI, because it flips to IN_REVIEW the moment someone opens it.
One thing I would not do: resubmit, swap the build, or edit the version in ways that require re-approval. All of that returns you to the back of the queue, and it is the most common reaction to exactly this situation.
I do not have an answer for an accepted expedite that produced nothing. That part sounds genuinely stuck, and the App Review team is the right escalation. Hope it moves soon.
