There was a problem in SPM12 readings its own GIfTI files.
See this other post:
This has been solved on the side SPM12 side long time ago.
In fact the SPM12 version you are using (SPM12 (v6217) is 10 years old.
We suggest you to remove SPM12 from you Matlab path, a let Brainstorm to install it as a plugin with the menu Plugins > spm12 > Install
https://neuroimage.usc.edu/brainstorm/Tutorials/Plugins
If you do not want Brainstorm to manage the installation of SPM12, once you have update SPM12 in you computed, add it to Brainstorm as a plugin, but using the Custom install option:
Manual install: If you already have a given plugin installed on your computer (eg. FieldTrip, SPM12) and don't want Brainstorm to manage the download/update or the Matlab path for you, reference it with the menu: Custom install > Set installation folder.