Error message:
[code=lua]
Error while running event AlertsList::on_tick (ID 0)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
AlertsList/control.lua:163: in function 'fill_table_with_speakers'
AlertsList/control.lua:208: in function 'draw_gui'
AlertsList/control.lua:245: in function <AlertsList/control.lua:242>
[/code]

I assume there is a missing check for "valid" while walking through all the speaker entities or something. Repro for me:

1. Place a new speaker.
2. Mine the speaker.

So, yeah, that simple. :)

No more updates on this mod? This bug seems to still be present as this post is older than the mod itself?