European servers

[saeedaisspecial]

But I do, and it's not only with dodging, things like using bane or fester right after using a DoT will cause the last DoT to not be spread/not be used for fester, or getting a skill cast interrupted for no reason (actually there is a reason: in the server side you're still casting the skill)

This is because the effects of an ability are tied to the animation, so the DoT will only become active (And therefore subject to Bane/Fester) once its animation completes. This is a design choice by the devs and not an issue to do with lag or latency at all.
Such a lack of understanding shows you might not know what you're talking about in other areas.