I found a bug - and if you run into this bug before I release 4.20, send me a note. I can fix it in your save-file.
I'll need more time testing this before I release it. Most likely the only change will be this bug fix.

The Bug: Many hours into the game, the game crashes reporting an invalid entity in dropItems.
Once it fails, a restart MIGHT fix the problem, but really it's a specific scenario that causes the failure that will eventually occur after playing for many house.
If you see this issue - send me a note and it'll light a fire under my butt to make this release.

I've been chasing bugs. I had inadvertently added a bug right at missile launch. I tried to add the new larger roboport to the researchable items, but have not yet made that an item you can use. So save before launching - I will hopefully get this release out very soon. Lots of testing completed. The age old crash that I've been chasing for a while is found and fixed in 4.2.00 release.

The bug: Seems to be around stone being added to an inventory, but the entity trying to add the item to their inventory is either a ghost or some non-entity. OK - sounds nutty, but these last bugs are gonna be tough ones. I can safely check if the entity we're asking to drop items is really an entity and not a ghost-entity. The ghost entity tends to happen when you drop a roboport on stone. The stone entity happens to me when I'm fighting biters, I suspect that I'm standing near stone when a biter destroys it, and this results in an inventory change event. Anyway - I have alot more to learn about all this, and am coming up to speed pretty quickly.