This happened to me too in an ARAM. I requested a trade and the person I was trying to trade with never accepted nor refused the trade. The trade stayed up till the game launched. But when trying to load the game I get this error:
"Unable to connect to the sever. Please <ahref= 'https://support.riotgames.com/hc/en-us/articles/201752664'target='_blank'><u>check your network connection</u></a> and attempt to reconnect to your game."
It is not my connection because I was able to log into an alt account and start a game fine. Once I started another game I logged and tried my main only to get this same error. The error persists until the game I am trying to join is over.