Hi Rif,
Just to be entirely sure, is it only one of your instances that is on 1.9.29 or is it all of them? Because if it's just a subset, it's expected.
1.9.29 is not fully released yet, and to make sure the future release doesn't break production for applications, we normally send some traffic from each project into an instance with the new runtime. This is built with a lot of roll-back possibilities, so that if that new runtime seems to generate errors for you, we can roll back and investigate. If too many applications report an increase in errors from the new runtime, the full roll-out stops.
This has been decided as more appropriate than releasing a rollout where an edge-case may mean that we miss the use-case of your application, and you end up on a runtime with no possibility of rolling back to a stable version.
I hope I've helped clarify this behavior :). When 1.9.29 hits full availability, we will release the notes on it :).
Cheers!