Line weight and Line color get lost

Thank you for your responses. I'm working with Illustrator for over 30 years by now. I never had that problem before. It happens since a few weeks only. Maybe it has to do with the regular updates. I'm using the swiss-german keyboard, therefore it could be a problem there. I had a large path with some "holes" (spots not to be filled) within this path. I put the holes into the foreground and the mainpath into the background. Then I selected all off them together and used the pathfinder symbol (the forth on the top row from the left) to connect all the pathes. I gave the path a color (10% black). so far everything went well like always. Then I hit the keyboard combination ctrl+alt +3 and everything showed up in the layer color, as long until I deselected all. After that I coudn't see the lines. Ok, I put the gray filled path into the background again with shift+ctrl+( . But I still saw no lines. Therefore I selected one of these lines and discovered, that it lost the weight and coler Information. The Line weights were 0.2 and 0.4 Points, the color were all 100% black, well, at least before I made them invisible with ctrl+3. I've got a very similar drawing to do, but I probably will finish it at the start of next week. I will be very careful to do everything right then and I will let you know what happened. Until then, I wish all of you a great week. Thank you.