Just to let u know we tried to replace a core miner who was active for every core seam on Nauvis with a Rare one (blue rarity) and this concluded in an instant Crash

got the error message for me?

The mod Space Exploration - core miner able to mine every seam surfacewide (1.0.2) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event se-core-miner-able-to-mine-every-seam-surfacewide::Custom event (ID 309)
LuaEntity API call when LuaEntity was invalid.
stack traceback:
[C]: in function 'index'
...-miner-able-to-mine-every-seam-surfacewide/control.lua:119: in function 'get_mining_target'
...-miner-able-to-mine-every-seam-surfacewide__/control.lua:125: in function 'update_amount'
...-miner-able-to-mine-every-seam-surfacewide__/control.lua:37: in function <...-miner-able-to-mine-every-seam-surfacewide__/control.lua:34>
stack traceback:
[C]: in function 'raise_event'
se-core-miner-efficiency-updated-event/control.lua:26: in function 'on_core_miners_equalized'
se-core-miner-efficiency-updated-event/control.lua:34: in function <se-core-miner-efficiency-updated-event/control.lua:29>

thats what i get printed as notice

blindly fixed it, let me know if the new version works or not.