Strange stability issues at specific times of day

I have been having strange stability issues on the Old Client when zoning, but only at specific times of the day, the problems start sometime in the morning and then disappear by late afternoon, at like around 5 PM CET.

Right now the game is basically unplayable for large chunks of the day as every time I zone there’s a 50/50 chance I will DC. This is especially frustrating as the problem persists on different connections at the office and at home.

This is my 3rd day with the problem. Yesterday I have done a full reinstall, today the problem cropped up again.

What could be causing this, and what could I do about it?

The recoup.

1, The problem only occurs in a certain time interval.
2, The problem persists across various internet connections.
3, A full reinstall did not fix the problem.

I suspect some form of file corruption.