@julie, thanks for raising this issue. While you may have second thoughts about the HDF5 2.0.0 update, you did what I would recommend to anyone without hesitation. Bravo!
We published an HDF5 2.0.0 Library Migration Guide that starts with four common “myths” about HDF5 2.0.0. What you are seeing, I believe, is a form of what’s referred to as myth no. 3 in the document: All files written by 2.0.0 are unreadable by 1.x. The solution provided in the document reads: “If you need older compatibility, explicitly set bounds.” Now that may sound a little mysterious, but an example is given a few lines earlier Example 3: Creating files that older HDF5 can read. Would you mind trying that and reporting back?
Best, G.