Tried to reproduce in a worst-case scenario: from R to P device, file shared with Bluetooth (had to zip/unzip it).
I can confirm the behavior you noticed 
Nevertheless, success came to me when using “Select” function from the awesome MiXplorer file manager 
:
MiXplorer official web page : https://mixplorer.com/.
Official download links : https://forum.xda-developers.com/t/app-2-2-mixplorer-v6-x-released-fully-featured-file-manager.1523691/ (file name is MiXplorer_v6.58.4_B22020910.apk).
Also available in add-ons storage at https://drive.google.com/drive/folders/1BfeK39boriHy-9q76eXLLqbCwfV17-Gv.
Side note: I didn’t notice any problem when selecting the file on the R device (where the JSON was generated)… Maybe a problem with old API?