Tried with all default parameters.
The screenshot has been created and saved in [root]/media/snapshots/nameofthecamera/ folder.
I can see the file from the Terminal, not from File Explorer add-on which can’t go back from /config.
I can’t see/load the picture from Media in the left HA menu because that folder is not shown at all.
I still receive a “failed to load attachment” in the Companion App.
About my config in the configuration.yaml, I followed this suggestions.
I believe that there are different behaviours based on the type of HA installation you have, mine is HASSOS.