Working on my third relic.

The times per second location is checked is clearly varied (prob for load balancing server use).
Test this by casting something and moving... and seeing how many decimals of a second pass before your spell is interrupted.

I usually see about .1 now a days (100 ms), a month ago it was easily 300 ms.

That means you had to be 300 MS ahead, and we still killed it. Easier now.

You are either slow, or laggy (pc or net lag).

I will assume slow. People overestimate their own ability to react because they can not perceive reacting faster (shocking). Thus thinking you moved as soon as possible. Just as people with faster reaction times have difficulty perceiving being unable to not react fast enough (and yelling at people for failing). Although practice helps because novel stimuli are perceived slower, the overall neural efficiency of a person might be a limit.

But the challenge can be fun for people who can do it... Can't make everyone happy.