When I copy and paste an object sometimes the object's stroke changes thickness

This has been going on for a couple of months. Preferences, everything has been reset and illustrator has been updated several times by adobe support team so I am here now for help. I draw many objects with the blob brush in their own file and then copy and paste them into a new file; then I will color the drawn object with the paint bucket tool and copy and paste it for use. Yet when I do this the pasted object's stroke changes thickness. Usually, it gets thinner but sometimes it gets thicker but it doesn't look to be the same thickness at all compared to the original object. It doesn't happen with all objects either but the workflow is the same for them. What should I be doing to prevent this? Thank you SO much for your help, hopefully soon.