I had some mud daubers completely block the blowby tube once. Lost a few gallons before I saw oil dripping down. I knew right then what it was. Those little red SOBs were building mud nests everywhere where I used to live.
Took my screwdriver and punched that slug of mud out. Those flying bleepers moved a lot of mud for their size.
OK, one thing not mentioned is fuel leaking into the oil. A bad injector can cause this, Happened to me and by the time we figured out the engine was toast. $19,000 later we are all better. Hope it is something simple but get an oil analysis done right away