I am not sure when this stared, but it has been happening for many months. If I would have to guess, probably around the time of the High Sierra update last Fall. When on a public wifi network, most commonly in a hotel, have to manually reconnect every time my computer goes into sleep mode, either because of the set sleep time or by closing the lid. This issue happens whether on a completely open network or those with login screens (again, such as in hotels). It is not timing out from the public network as when I do manually reconnect I am not asked to re-authenticate (such as entering my name and hotel room number). At home, I automatically reconnect. Any ideas? Thanks in advance.