I may be able to fill in on this one.
If I may ask a few more questions before I proceed with my train of thought.
Where are you when the problem occurs?
What is your ping to the server? Do you know how to go to Command Prompt and get a ping readout?
Do you currently have any mods on your client?
And lastly, did you happen to feed a little fluffy creature after midnight and let it go play in the rain? Because I think you may have a case of gremlins tampering with your gear.