I have only noticed this on custom maps that I make but at some point the builders stop building anything no matter how many times I cancel and rebuild or destroy and build more builders. More than half of the map worth of resources disappear and whatever is left glitches and allows the rovers and bots to travel through most of them. Not sure if this is related but I haven’t been able to export any of the maps I make to my iPhone to have a custom map for each planet type. Haven’t tried with a regular map yet but don’t want to get into one just to have it turn unplayable.