When Funnel asks you to reconnect a source, it could be for many different reasons such as that someone has change the credentials to an account that is connected to Funnel. Another example is that a platform has made changes in the API which require you to reconnect that source. Why your data source needs to be reconnected will be explained in text on the data sources page.
You can also reconnect your data source without Funnel telling you to. A reason for doing this could be that you might want to use other credentials for a source. The person connected to this connection might have a change in permissions in that platform or might be leaving her or his position.
Note that reconnecting a source will not re-download historical data, it will simply just verify the connection and furthermore start download data again. Also note that when you reconnect, data will be imported at the next scheduled try. If your data doesn't immediately start download, wait a couple of hours and check again. So if you need all historical data from that data source to be re-downloaded, you need to contact support and we will trigger this for you, since this is not something you can do yourself.