Please see https://forums.factorio.com/viewtopic.php?f=7&t=73488 for the full details, and save.

The assertion is that you cannot mix fluids, and with the latest version of the mod, they are mixed.

After upgrading to the most recent version the game asserts when loading the map: I had the older version installed, with no errors, so I assume that something changed to intermix fluids where they had not previously been connected.

I ... don't actually expect you to fix this, necessarily, but would rather tell you than decide if you care on your behalf.

I do certainly care about this, however, a crash to desktop is always a refer to Wube.
Do you know what version of APP that you upgraded from?

I think I have an idea of what might have caused it - but it shouldn't cause a CTD.

For anyone following at home: is now resolved, and thanks to the mysterious stranger for working hard on it. Wube, I believe, are also going to fix the fact it was possible to trigger the assertion, but ... IDK. something. but anyway, is resolved now.