I created some reports in Visual Studio 2015 with all the latest updates. However, when I try to deploy the reports I get this message:
The definition
I actually ran into a similar problem where a change I needed to make resulted in an "Undocumented Error/Invalid RDL Structure" error in 2016, so I edited the RDL file so I could open it in an earlier version and make my changes. Not too hard, but you need to make a couple of tag edits.
For new reports you should probably just use an older version, but for existing reports you can do this: (I reverted to 2008)
Actually wrote some superhackish code to do this as part of a blog post, but the manual edit is simple enough.