I updated to 1.4 and my Krastorio 2 Spaced Out save now clashes. Updated to 1.4.1 just in case and looks like the issue is due to the drills. here is my error message

Failed to load mods: Error while running setup for entity prototype "electric-mining-drill" (mining-drill): next_upgrade target (electric_mining_drill_mk_2) must have the same fast_replaceable_group (mining-drill != electric-mining-drill).
Mods to be disabled:
space-age (2.0.60)
. Krastorio2-spaced-out (1.4.18)
. squeak-through-2 (0.1.2)
. tech_tree_plus (1.4.1)
· Krastorio2-spaced-out (1.4.18)

Thank you for reporting it.

The vanilla "electric mining drill" has a "fast_replaceable_group" set as "mining-drill"
Krastorio has "electric-mining-drill"
And since mine "electric mining drill mk 2" is a copy of the vanilla one it crashes.
(or something like that)

This also expands to other items (electric furnace).

For now the fix is simply to disable "next_upgrade" flag for the mk2 items. This means you have to manually upgrade them with the upgrade planner.
If there are more problems, let me know. If the changes become too great (like this mod) I will have to unfortunately put it into "incompatible" category.

Version 1.4.2