That's not lag, that's a bug with Biotic Charge. It happens when you try to charge, but die during the latency before the charge activates. Your client thinks you charged, but the server thinks you didn't. This causes synchronization issues for the rest of the match; the only way to fix it is to quit and rejoin. Of course, that's not really an option if you're playing a public game.
This isn't lag either. The exact cause isn't as easy to pin down as the first bug, but I believe it's randomly triggered by Nova. Each Nova has a chance to simply lock you out of using any abilities; you won't be able to Biotic Charge, Nova, or Shockwave. Usually, taking another action will fix it; firing your weapon works just as well as rolling, and is much faster.
This second bug is why shotgun Vanguards are currently terrible. The low fire speed and small clip make it difficult to fix the bug, so you can't always get your charges off when you need to. If you need to charge when your clip is empty, and the bug triggers, it generally means death. If you have to use a shotgun, a Scimitar is probably your best bet. Personally, I've started using a Tempest; fast fire speed and huge clip makes it easy to work around the bug. A Phalanx or Predator works too, but make sure you don't empty your clip until you're in a safe location.
