After upgrading to SketchUp Pro 2018 I opened the Extension Warehouse, My Extensions page, and found several problems. Most important to me is that my license for 2DXY SlickMoves has disappeared from the list of paid &/or installed extensions.
Mystery solved by the 2DXY developer. Other customers have had a similar problem to mine, self-inflicted double account. I thought when signing up with a new computer that I had edited my email and password. Turns out that I opened a second account.
I’ll ask Trimble if they are able to combine the two.