I've heard of this problem before, and the suggested reasons, but I don't think any of them apply in this case.
According to the answer to this question, the edit link will disappear if:
- You are not logged on and the post is 12 hours old or less
- There is already a pending edit on this post
- The queue is full, only happens rarely on new SE sites with no moderators
- You have been banned for a week cause you submitted many rejected edits
The first reason isn't applicable. I was doing reviews.
The second reason isn't applicable. It is happening for all questions/answers.
The third reason isn't applicable. This is on StackOverflow. Pretty established, plenty of moderators.
The fourth reason shouldn't be applicable. I'm pretty sure every last one of my edits was approved, based on my reputation increases, though I didn't keep track. If this is the reason, the threshold has to be really low--no more than 10% of my revisions could have been bad edits. (Is there any way I can check this to be sure?)
So, what could be the cause of this?