90K connection issues when playing FFXIV

[Pyrolanthic]

ISP:
Telenet N.V., Belgium

Type of Internet Connection:
Optic fiber, using Cable

Internet Connection Speed:
200 Mbits/s down, 12 Mbits/s up (these are max, reality is around 180 Mbits/s down, 10 Mbits/s up)

Date & Time:
Since last week, timezone GMT+1, happens after being 5 to 20 mins in game. Usually play between 2PM and 3AM local time with this issue constantly happening.

Frequency:
Always since a week ago

Character Name:
Ayo'a Ibori

World:
Zodiark

Area and Coordinates:
Any map, any area, any coordinate, any dungeon, any trial, ...

Party or Solo:
Solo and party (4)

NPC Name:
None

Monster Name:
Any

In-Game Time:
Happens so frequently I didn't note this down. Happens every 5 to 20 minutes approx. Mostly during in-game daytime I suppose?

Steps:
1) Log in
2) Select character
3) Play game (walking/running/battle/chocobo/FATE/registering on Duty finder/being in a Dungeon/ doing a Leve/questing)
4) Get disconnected about 5 to 20 minutes in, error message 90001
5) Return to character select; start again at 2)

PC Specs
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Windows 8.1
Intel(R) Core(TM) i7-3770 CPU @ 3,40Ghz
RAM: 8,00 GB
x64-processor
NVIDIA GeForce GTX 760