AFTER TYPING A LONG EXPLANTION BELOW.... here is the solution.
I'm guessing that people who are having this problem have their Permalink settings set to "Post Name".
If this is true in your case, the following worked to correct our Job Manager problem of not displaying the jobs or applications.
After updating to WP 3.5 go to Setting > Permalinks
Change the setting to "Numeric" and hit update.
Change the setting back to "Post Name" and hit update.
Viola! You should be able to view your jobs and applications now....
For kicks you can read our problem below that was corrected with the above adjustment.
I have the same issue.
I started by deactivating the plugin and reactivating it. Didn't fix anything.
Kept seeing only the "if you plug in worked you'd see the proper stuff on this page" text.
So I went to that page in our case /about-us/jobs and unpublished the page by changing the status from "Published" to "Draft".
I then changed the Display Settings in Job Manager Settings to show 10 jobs at one time (we only have 4 openings) so this was just a test.
Now the jobs show up and the url has reverted back to the /?page_id=204 format where as the rest of our site runs on the /about-us/jobs/apply/575/ format which explains why it cannot find page to post as it is looking to use the post number, not the alpha equivalent.
Perhaps there is a need to revert a site back to the numeric page labeling or a need correct a setting within Job Manager so that it can function on the title page labeling method.
Example: (THIS WILL NO LONGER WORK AS WE CORRECTED THE PROBLEM)
You can now see out jobs listed here... http://cleaningheroes.wpengine.com/?page_id=204
But when you click the apply now button the url seeks the "/about-us/jobs" extension which it cannot locate despite our setting having not changed.