There are definitely some networking issues in GT7. However PD would claim that your/others internet connections are not their responsibility.
Earlier this week we tested the connection from my Ps4 Pro to TJCs lobby. There was a little bit of lag but nothing unusual, and players just need to get used to driving with some lag, because it will never be perfect. It's not possible to have zero lag on an internet game.
Glitches are different though (and I did have a major glitch, more on this later). How GT7 manages missed data packets is up to the programmers, but I imagine it's a difficult problem to try and provide the fastest possible data transfer between the PlayStations and continually check for lost packets at the same time. Somewhere they must make a compromise, but with the wide variation of speeds across the globe, where do you draw the line.
As mentioned in Famine's pinned article, the best thing you can do is optimise your connection, and then hope that everything works.
Regarding the glitch mentioned above, it turns out that my hardware was the cause. When the race was initiated my PlayStation went to full black screen and no buttons worked (other than exit). The entire lobby hung, waiting for my PlayStation to connect. Realising the problem, I closed the GT7 application from the PlayStation menu and the lobby (minus me) immediately started the race for all the other players. This happened several times, even if I was only spectating, the lobby would hang, however my friend who lives next door had no problem at all. He's also on Ps4 Pro and with the same internet provider, and connected to the same lobby. So it was clear that the problem was at my end.
I reset my router, cleared the game cache, set the IP address to Automatic and rebuilt the PlayStation database, but it didn't make any difference, the lobby still hung whenever I was in it and the race was initiated.
Then it occurred to me that years ago I had set up Port Forwarding in my router, for GTSport! I did a full hardware reset of the router, back to default settings (tiny button to press with pin), which cleared the port forwarding from my router (I couldn't be bothered to connect by pc) and...... Whallah!! Re-joined the lobby and was able to race with no glitch.
This needs further testing to confirm direct cause & resolution, but I did find a site that showed the Port Forwarding requirements for GT7 is different to GTS! One port was extra on GTS, so it's possible that this could cause a glitch in p2p connections in GT7. Again I note that this needs further testing, or perhaps some comments from those who know more about routers than me.
So,
@RacinLei, let's check your end...
1. Are you using cable or wifi connection to your PlayStation?
2. Have you confirmed that you have NAT2 connection (Network Settings > Test Connection)?
3. Have you set up port forwarding in your router, for any online games?
4. Probably worth reading Famine's pinned post (Connection Issues), to see if I've missed something, and also test your connection in Sport mode (Test button - top right) to confirm your pentgon is all green