Esri Support, Jon Pedder (@Jon Pedder), and myself are working on isolating this issue, but it is in fact not an ArcGIS Pro issue. Most likely a custom symbology or projection issue with how the MapSAR template has been compiled. I will post more details later.
I did try IGT4SAR / MapSAR Extended (Don Ferguson) and Pro was successfully able to import the mxd and edit: dferguso/MapSAR_Ex · GitHub