Unexplicable multiplayer desync issue (did not happen before)

[true gokturk]

I ususally play arma 2 OA v 1.62 with a few (actually alot of) mods. Sometimes i like starting up a server for my friend to join.
Now, 2-3 days ago everything worked perfectly fine with acceptable lag.
Today, as soon as the mission starts his desync shoots from 0 to ludicrous numbers such as 10000, while his ping stays at an acceptable 80.

I found that our mods load order and a few pbos were mismatched. But even after fixing these the desync stayed (not to mention, it did not happen before)

When i tried vanilla arma 2 (not arrowhead), his desync hovered at 12 instead.
Why? What to do?
I am quite sure it is not the mods fault as this did not happen before.