im not that supergood blocker (2h), but for all my fail blocks I found my fault,
like bad angle, released block for a moment (which opens your defense), etc.
With unstable bandwith (when others are using net on my lan),
very rarely I see that my attack is going through the enemy without collision.
Maybe packet losses, the block problem could be related to this.
In general, I don't face this problem, but make sure for example in the case of side swings, that
your blade is between your body and the enemy's blade, not only in the proper direction,
and during block, use also your ears and instincts, not only your eyes.