Thanks for the extensive testing on this front!
There are some artifacts to the currently available geological time implementation – particularly notable when resolution is not a power-of-two-plus-one.
The good news is, I’ve actually just finished some work extending the framework to be much more stable across all resolutions – this should fix this issue, and also in particular help with making erosion much more consistent across resolution scales. You will be able to choose to use the new or old version.
More details to come – the next dev channel release is going to be a monster of a feature release
And in the meantime, I would recommend solving your problem by either not using geological time in this particular map scenario, or perform two erosions; one without to do the borders properly, and another with but with the borders masked out so that it doesnt’ effect them.