https://wccftech.com/black-ops-cold-war-warzone-pc-crossplay-disabled-zed-398-swift-clover-error/

Call of Duty: Black Ops Cold War and Warzone PC crossplay has been temporarily disabled as developer Treyarch is looking into the ‘Zed 398 Swift Clover’ error that players are experiencing.

Yesterday, the new Cold War update went live followed by a separate patch for Warzone this morning. This update merged Warzone with the latest Call of Duty installment and introduced the new Season One content, but apparently, the new update is causing an unforeseen problem for players attempting to play the Season One content.