That's why you start with just UC and the map, then add just mods that add productions and fillTypes on a new save. Leave the other 1300+ disabled. The vast majority of those mods are irrelevant to this test and can be ignored. Not sure how many production placeable mods you have, but 90% sure of of them is the culprit, especially ones that add new fillTypes.
In other words, out of your 1500 mods (at least from the list I saw), only maybe 10% of them could possibly be causing the issue. So, you don't have to test every single one.
The idea is to start with just one mod (the map), see if it works with only that enabled. Add a mod or two (only the types I mentioned above), try again. When it breaks, you know it was one of the last batch you just added. You could even do 5 - 10 at a time, at least it would narrow the range from 1500 to 10, which would be much easier to needle down on.
Edit: Or you could just wait until I finish the next version and see if it resolves the issue. No eta on that yet though, still a lot of RL things I'm dealing with. This is a work around for "in the meantime".