Sometimes the client will get into a disconnect state without any indication. If you find that your opponent is taking too long to move, how long depends on the time control , refreshing the browser, if you are on the website, will often force the reconnection.
If you are on v2 then switching to v3 may also help.
It happen already twice to me to loose a game with written that I abandoned the game, while no internet problem was appearing and my clock was on stop and the opponent clock was running down...
What is the problem?