Hard crash when exiting sandbox. I dont know how to replicate, but its happened to me twice after AFKing in a sandbox for a VERY long time. Will post this under both mods.

The mod Blueprint Sandboxes (2.1.5) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event blueprint-sandboxes::on_lua_shortcut (ID 37)
The mod miniMAXIme: Character scaler and selector (2.0.4) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event minime::on_player_changed_force (ID 60)
bool expected, got nil
stack traceback:
[C]: in function 'newindex'
__minime/scripts/gui_stuff/gui_available_chars.lua:901: in function 'unhide_gui'
minime/scripts/gui.lua:208: in function 'enable_guis'
minime/scripts/forces.lua:280: in function 'event_handler'
minime/scripts/events.lua:288: in function <minime/scripts/events.lua:285>
stack traceback:
[C]: in function 'set_controller'
blueprint-sandboxes/scripts/sandbox.lua:277: in function 'RecoverPlayerCharacter'
blueprint-sandboxes/scripts/sandbox.lua:228: in function 'Exit'
blueprint-sandboxes/scripts/sandbox.lua:440: in function 'Toggle'
blueprint-sandboxes/scripts/toggle-gui.lua:231: in function <blueprint-sandboxes/scripts/toggle-gui.lua:229>

If I disable Minimax, and leave the sandbox I get the message "Unfortunately, your previous character was lost, so it had to be recreated." It looks like thats the case with minimax enabled as I dont have armour but the message doesn't get displayed.

Minimax is the mod causing the crash - not this mod. However, I'll need some replication steps to know why the old character isn't valid anymore, otherwise I cannot attempt to resolve that.