I was unaware that this family of mods was changing the types of my game save turret entities. eg: "laser-turret" is now "laser-turret-purple". Loading a megabase save leads to several thousand "laser-turret-purple" entities being deleted now that this entity type is no longer part of the mod. The 0.12 version of the mod is not compatible with this version.

A simple fix is to add a migration script for the items and entities. For me, "laser-turret-purple" -> "laser-turret" was enough but other game saves might need the others.

I fixed this BTW, the mod now contains the migration needed to prevent this

Thanks Klonan. I will reinstall now that it won't delete my laser turrets any more :)