Appeared after updating mods and loading my existing save.
I'm still investigating if a mod conflict could be the cause. I've confirmed that it's possible to start a new game even with the same mod list, but it's also true that the subsurfaces don't get generated until you try to interact with them in some way, so I'm working on investigating if a 1.1.5 -> 1.1.6 update is necessary to replicate it (at least editor mode can speed it up a bit).

The mod Subsurface - build beneath your base! (1.1.6) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Subsurface::on_configuration_changed
Subsurface/scripts/resources.lua:105: attempt to index field 'entity' (a nil value)
stack traceback:
Subsurface/scripts/resources.lua:105: in function 'copy_resource_data'
Subsurface/control.lua:96: in function <Subsurface/control.lua:70>

This error is unlikely to be caused by an update 1.1.5->1.1.6 because the referred field existed in the previous version.
Do you have any progress in investigating?

I just tested starting a new save on 1.1.5 with only Space Age + Subsurface, and played it far enough to have a subsurface before updating to 1.1.6, which was not sufficient to replicate the issue. The next thing I'll test is creating a subsurface on every vanilla planet.

Initial test results show that 1.1.6 doesn't like Gleba. Best guess: from the sounds of things it's trying to copy resources from the surface to the subsurface. I suspect it may occur when it attempts to do this with a surface that doesn't have any resources to copy over, as a subsurface will never contain stone patches, which are the only ore patches that spawn on Gleba.

Youre right, if theres only stone, nothing can spawn in subsurfaces