Had a similar issue today - downloaded the manager from my speckle.xyz home page (just made my account), installed, upon opening the manager was immediately notified that a new version is out, installed that, manager refused to start from then on. Solution was to uninstall everything, download from here, then it worked for some reason.
Hey! FYI as the Manager 2.3.18 comes out we faced the same issue. The manager automatically triggers the update, closes it self promising that will launch the updater but nothing happens. Downloading the latest installer from the releases page and reinstalling works, but does not feel ~great~, if you know what I mean.