If your node is detected as offline by the satellites, they will no longer suggest your node to uplinks as an upload target until the satellite has verified that your node is online again. Currently those uptime checks are happening at random intervals I believe and the method is the same for online and offline nodes.
Changes are planned that will increase the frequency of uptime checks by a lot for nodes that are offline, so it can be detected much more quickly when nodes are back online.
More info here on the discussed/planned changes:
tl;dr: Don’t worry about it, traffic will return as soon as the satellites have performed a new uptime check. Usually within an hour or 2. Do keep in mind though that testing and usage can be intermittent as well, so times with no or little traffic can happen.