https://www.gamespot.com/articles/overwatch-patch-notes-for-ps4-xbox-one-and-pc-cove/1100-6456789/

As Overwatch's Year of the Dog event continues, Blizzard has released a new patch for hero shooter that makes changes to Lucio's abilities, fixes bugs, and more. Starting with the hero updates, Lucio's Wall Ride ability will now cause him to drop the flag during CTF matches. Blizzard explained that the Wall Ride ability made it "overly difficult" to stop Lucio in Capture the Flag matches because he could reach "unintended places." Now, using this ability will cause him to drop the flag and this should result in better balance, Blizzard said.

As announced previously, some abilities involving mobility and invulnerability will cause you to drop the flag. For example, Winston's leap/jump pack ability results in a dropped flag. Blizzard's thinking here is that CTF matches will be more "action-packed" and fun with these particular abilities restricted.