Error while running event tree-growth-natural-expansion::on_tick (ID 0)
LuaTile API call when LuaTile was invalid.
stack traceback:
tree-growth-natural-expansion/control/expansion.lua:127: in function 'tryToSpawnTreeNearTree'
tree-growth-natural-expansion/control/expansion.lua:279: in function 'processTreesInChunk'
tree-growth-natural-expansion/control/expansion.lua:305: in function '?'
tree-growth-natural-expansion/control.lua:29: in function <tree-growth-natural-expansion/control.lua:26>
stack traceback:
[C]: in function 'index'
__tree-growth-natural-expansion/control/expansion.lua:127: in function 'tryToSpawnTreeNearTree'
tree-growth-natural-expansion/control/expansion.lua:279: in function 'processTreesInChunk'
tree-growth-natural-expansion/control/expansion.lua:305: in function '?'
tree-growth-natural-expansion/control.lua:29: in function <tree-growth-natural-expansion/control.lua:26

Can you tell me which, if any, other mods you have enabled?

It was "Delete empty chunks". This is happening some time after removal of the chunks

There is a setting in bot Delete empty Chunks and Tree Growh Natural Expansion which refers to the distance of chunks.
By default it is 2 in DeC while in TGNE it is 3. Essentially this means that TGNE will try to expand tree chunks outwards but DeC will delete the third chunk. This causes some issues. I would recommend to reduce the distance setting in TGNE accordingly.

Unfortunately I was not able to reproduce this case, however I added a valid check so this should not happen again.
(2.4.1)

Thank's!