Seemingly as of the latest update, this mod doesn't work consistently. Planting saplings is a crapshoot but mostly they no longer grow into trees, sometimes they do and sometimes they don't, most of the time they don't. Here for instance, all of these were planted at the same time a long time ago.

https://i.imgur.com/nPdaUxQ.png

I think I figured out the problem by happenstance - it seems that trees placed with the Nanobots mod don't grow, but they do if placed manually (in my previous playfile using the mod, by the time I installed it I had moved on to roboports). I'm not sure what the conflict is or if it would be on your end or the Nanobot maker's to see what can be done to fix it.

https://mods.factorio.com/mod/Nanobots