I have worked with the presentation file shared by you and have been able to observe the issue of missing table header row in exported presentations. An issue with ID SLIDESREP-33181 has been created in our issue tracking system to further investigate and resolve the issue. This thread has been linked with the issue so that you may be automatically notified once the issue will be resolved.
I'm trying to find a work around for this problem, please let me know if you have any suggestions. I don't want to change the tablix position to create the Indentation because I want the header row's background color to go all the way from edge to edge.
I have also been able to observed the missing indent properties in exported presentations and an issue with ID SLIDESREP-33182 has been created to resolve the issue. This thread has been linked with the issue so that you may be automatically notified once the issue will be resolved. I regret to share that presently, I may not offer any work around for you in this regard. If you do find one, please share with us as well for our reference.