I don't think you can really do much about this, but wanted to put up a thread so others might know what's going on without digging into the code. I used a lot of balancers in my game, probably more than is reasonable, so the migration in 1.14 results in what appears to be freezing on game load. Or at least I think that's whats happening, I can't directly confirm that it's sitting in the migration but since it is looping over every balancer entity and I probably have thousands it seems likely. It took about 30 minutes to run for me.

I had Bugs in the code, that in some circumstances, the balancer wouldnt be registered as balancer. The only way to have it fixed, is to recreate every Balancer and therefore i have to iterate over every balancer-part and recreate the Balancer itself.

This should normally not run about 30 minutes. On my maps it only took up to 30 seconds. I cant really change things about that, i think. Just out of interest, can i have your map? I want to see how perfomant it runs with a lot of Balancers running actively.

Pardon the long links:

Before the upgrade

https://coderanger-factorio.s3.us-east-1.amazonaws.com/before-bb-upgrade.zip?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAJTFVUEZFU7LF6YOQ/20191222/us-east-1/s3/aws4_request&X-Amz-Date=20191222T235036Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=bd322c2b805b0dadbb88d72252844287c733de5db96d38e8ce56ef92ad1b23eb

After the upgrade (taken right now):

https://coderanger-factorio.s3.us-east-1.amazonaws.com/after-bb-upgrade.zip?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAJTFVUEZFU7LF6YOQ/20191222/us-east-1/s3/aws4_request&X-Amz-Date=20191222T235111Z&X-Amz-Expires=604800&X-Amz-SignedHeaders=host&X-Amz-Signature=be9b3371a88871a682f6536e6b32633b53efc36e6904f23ece8c06d4b70004e9

I'll very much admit to abusing balancer as basically object pipes, you can see I've slowly shifted my factory designs away from it to keep my UPS happier though.

That maps looks cool :) I wish my maps would look like that and not like a mayhem and chaotic.
Just for your interest:
You've created 128 Balancers, with 31591 Balancer-Parts.

When you migrated that map, it had to iterate over all 31591 Balancer-Parts and rebuild the balancers, thats why it took so long.

Yep, once I pulled up the diff and saw the migration I was pretty sure that was the issue. Just unfortunate that Factorio doesn't show any kind of UI feedback that a migration is running so I figured some other users that could be less familiar with Github might be confused or worried that something is broken :)

Also props for solid coding that I can run that many balancers and still get around 45-50 UPS on my gaming PC!

This issue moved from 1.1.4 to 1.2.0/2.1.0.
The Migration to 1.1.4 is removed.