After updating to Illustrator 25.2.1 I have noticed that (sometimes) the colour assigned to an item (stroke/fill) can be changed, seemingly randomly, to another (similar looking) colour. I am copying and pasting newly created items in the same document. e.g. Create new box assign spot colour stroke. Copy. Paste. New item is assigned CMYK. If I paste a second time its OK.
No. Colour setting on 'Europe Prepress 3'
Yes. So far I've only noticed user created spots changing. ie Rich Black.
So here is an update. Today PMS colours created from Illustrator swatch (colour books) changed to CMYK on pasting. Unlike previously the correct (PMS) colour did not appear on re-pasting.
You paste from one Illustrator cmyk document to another, or add them from a library?