This mod and Secretas&Frozeta planet mod both define global noise expressions named

mountain_volcano_spots
mountain_plasma
mountain_elevation
mountain_lava_spots
mountain_basis_noise
volcano_inverted_peak

(it seems you both copied from the Vulcanus preset)

Currently they resolve to the same results, so nothing breaks, but whichever mod loads later silently overrides the other's.
Prefixing them with the planet name (like already done with all other entries in those files) would avoid potential future issues if either mod changes its mountain code. (And avoid potential issues with other mods, I currently only checked a few and these two had the conflict.)

I assume this is just an oversight and I will report it to Secretas&Frozeta as well.

I'll check it out.

Also, to add background, Rubia and Secretas both started off a copy of Zach's Corrundum, which copied off Vulcanus.