Test Network ping is different from in-game ping

I'm on Ultimate tier, only gaming with ethernet cable.

I usually manually select the EU Southwest server to play, however I notice that when I click on Test Network I have like 26ms of ping, 0 packet loss, etc...

But sometimes when I'm in game as soon as the session starts I immediately have higher ping (from 25-26ms of the test to 60-70ms in-game) and huge packet losses. So what I do is end the session as soon as it starts and connect again on the same server, and my problems are solved. Why this kind of stuff happens? Sometimes I even need to restart the session a lot of times to get one with my actual ping.

Is this happening to anybody else?