@3-14152898 Do you have `files.use_atomic_file_saving` enabled under Preferences->Various? If I'm not mistaken, it's not enabled by default and with the normal `fwrite()` method that Geany uses otherwise it might happen that when you shutdown your system, the written data won't get flushed to the disk.
I was able to reproduce similar problem locally when my LSP plugin was crashing on unload during Geany termination which caused that session files weren't saved in this case and the whole session was lost.
I think Geany should _really_ use `g_file_set_contents()` for saving all the config files to avoid problems like this.