leu_deu Thank you for clarifying. Based on the information you provided, we investigated and confirmed that the issue can be reproduced both when installing the spine-godot GDExtension and when downloading the 4.5.1 custom build. We have created an issue ticket for this problem's fix: EsotericSoftware/spine-runtimes2985
Incidentally, when I tested it with a custom build of Godot 3.6.2, it couldn't import files with the .json extension at all. Therefore, my personal guess is that while the .json file format itself was supported since some version (likely 4.x), the spine-godot side may not have been properly updated to handle it correctly, resulting in crashes.
We apologize for the inconvenience and appreciate your patience as we work to resolve this matter.
