Black regions on landscape tiles with 3+ complex layers

First off, this does not happen on my windows desktop - just the linux laptop.

This issue in a nutshell, is that when I paint a third layer onto a single segment of landscape, the shader will recompile, and leave that square black.
screenshot attached

Re-creating a very simple landscape material, (with identical blending settings this issue does not happen.
The issue occurs both in the editor, and in a packaged build.
Disconnecting the normals OR the base colour in the landscape material stops the issue from occuring
replacing the input normalmaps with world normal one-by-one will at some point solve the issue
replacing the inputtexturemaps with a plain colour one-by-one will at some point solve the issue

This makes me suspect the issue is when the shader complexity is too high (the basecolour and normal maps are fairly complex setups)

Is this a known issue? Should I just try and simplify my landscape material? Or is more investigation perhaps in order?

Laptop specs:
Geforce 970m
intel i7
32gb ram
linux (ubuntu based)

Desktop specs:
Geforce 1080ti
intel i5
32gb ram