I can't get hydrogen from steam recipe to work after updating to 2.1, it's rejecting the 500 steam I put in as an incompatible fluid whenever I reconnect the pipe. It seems that the recipe calls for ">=500 steam" and I have 50-500 steam that's currently at 500 temp but isn't the correct fluid.

Flushing the pipeline and replacing EM Plant and nearby pipes doesn't seem to help. I was able to make a working test example so I will just have to deconstruct rebuild the entire pipeline I guess for now.

Update, upon further testing the problem is between the recipe and pressure forges. 500 steam starts out in a quantum superposition between 50-500 steam and 500-1k steam. Introducing the steam to the recipe first collapses the wave function and murders the pressure forges favorite kitty or something.

You have to choose, do you want to make hydrogen gas or power pressure forges. It turns out a solution is to build a contraption with 2 filtered pumps coming off of a supply of quantum super-steam and set the filters by selecting the steam icon on the recipe for one and select the steam icon on the pressure forge for the other pump. Route pipes accordingly.

I believe this is this Factorio bug.

I have the same problem; was appearing mostly for steam even on my space platforms. Right now seems fixed everywhere apart from Crucible, so we probably need to wait for Wube to fix it, is not depending on the mods

In the meantime, you can try deconstructing all the pressure forges on a surface then putting them back. That worked on a save I was testing with. But yes, Wube will fix the issue sooner or later.