Ever since the bullet reporters test build I have often encountered this bug where the LOST THE FLAG message is delayed by many seconds. In 5.12 this has not been occuring less, perhaps even more. It seems to happen more often with people with less stable connections. Gameplay-wise the biggest issue isn't even the moment when the message is not appearing, since you can at least still see the kill message, but when it is appearing. Since its so much later it could coincide with another flag loss from another player, creating a lot of chaos and confusion (on your screen).

An example:

Here is another example of multiple delayed&missing messages (and desync???): https://imgur.com/fIm0JXe
Ms roasts kev, but theres no message that kev lost flag and kev keeps the yellow flag star at his nickname, even after a7med recaptures. Also spyro makes the score but keeps the yellow star at his nick. MS captures, gets killed immediately by zolika but there?s again no flagloss message and yellow star is still at spyro?s nickname. Afterwards, spyro recaptures, loses flag again without flagloss message and lina recaptures, but yellow flag star is still with spyro. Then suddenly some of the missing flagloss messages appear on the screen together, eventho MS didnt even have the flag anymore. That?s when the yellow stars get updated finally in the playerlist.
U can watch the scene here at video timer 1:21:15-1:21:35: https://www.youtube.com/watch?v=lsdYI2aE8I0&t=4833s
This was in pxi intervall testbuild but with the exact settings which 5.12 uses now (/bulletvictim off and 0/0).