Name of Internet Service Provider (ISP)
Orange

Country of residence
France

When does the problem occur (e.g. only during specific times such as in the evenings?)
more or less constant, but the symptoms are a lot more acute during peak time (evening)

Frequency of problem (e.g. every 2 minutes)
More or less random, but still regular enough (every five minutes at most).

Game content in which the issues occur (e.g. dungeons, trials, certain areas)
More or less everything, I feel it a lot more in instances but it could be just be doing things more sensible to latency there.

The exact symptoms are network packet loss and a lot of rubber banding, I can move my character around and cast skills, but nothing network-based works, the world is frozen, using skills doesn't trigger any proc or combo. I can only guess I appear frozen with the red "disconnecting" status to other people at this point. Most of the freezes only last a few seconds, but now and then it can go as far as 30s-1min.

Since I happen to rent a dedicated server at Online, I took some time to setup an OpenVPN-based tunnel on it and it completely solved the packet loss issue. The game is near unplayable for combat content without it.