Material node error after transfering 'Undefined'

[gugusheep]

Hey there.
More often than ever I encounter this problem:

My material get ruined after opening the file on a different PC…
I suspect it is connected to the new Blender 3.5 update and the fact, that file saved in 3.5 and opened in 3.4 on another desktop may read the node as in the attached screenshot.
However I have updated both desktops to 3.5 and the problem occurs anyways.
Can anybody help me or hint an idea on what is the main cause? How do I prevent this? I render the scenes often on the second PC…
Usually a mix shader stops working and shows as a red “Undefined”
This makes the node not letting the information through so the result is white or black material…very annoying…
I haven’t had this problem before 3.5 update!!! Though my workflow was the same, always modeling it on one PC, transferring and rendering on the other…

[DNorman]

The “colour mix” shader was changed, the new version (“Mix”) allows you to mix floats and vectors as well as colours. I think if you open an old file with the new version it gets updated automatically but not the reverse.
ie If you open a new file with an older version of Blender you will get that “undefined” thing.