We did some further analysis and noticed that the issue is not related to the loading of this file.

After playing the game a longer time at some point the engine isn't able to load or save any file.
As we load the specBumb.fx with every room change, it's just the most common file operation.

Though levels, their models etc. are still be loaded, commands like "file_open_read" return no valid handle.

At this point a "file_save" leads directly into an engine crash.

Any suggestion where to search? Any hint why the engine can't read or write any file anymore?