The way SubSidekick works is that we send alerts to you for any and everything that hits your specific sub page while our server is able to be searching it. There are a couple different reasons why a job may hit your sub page (or you will hear about the job from someone else), but you still don't get an alert from us.
1) Server Timing: Our server searches your substitute page every 60 seconds (which is a timeframe dictated to us by the sub services). In between these searches, it IS possible for a job to come onto your sub page and be accepted by another user before our server is able to detect it. If that's the case, the job is no longer in the system when our server searches again, and therefore no alert is sent. These usually happen when the other sub happens to be looking at the sub website at the time the job pops up. However, if a job comes up or is still there while our server IS searching, we are able to send it to you within 1 second of detection, so most of the time we are able to get the alert to you.
2) Preferred Assignments: As you may know, there might be times a teacher requests another specific sub, and in that case won't put the job in the sub system for all to see. In this case they instead set up the job directly through the sub themselves and it won't ever hit your sub page for our server to see, and thus no alert will be sent.
3) Filters: If you didn't get a job alert that you think you should've, make sure you check your filters on both SubSidekick and your sub service (Aesop, SmartFindExpress, SubFinder, etc..). It may have been filtered out based on your preferences. You can always change your preferences if you'd rather see more alerts than you are currently seeing.