BARONBONGHITS: Same situation here. Pretty damn annoying bug, closing the hanging login window leaving invisible hanging processes is a nice touch :V
Definitive easy fast fix without reinstalling client or anything: Delete the file C:\ProgramData\GOG.com\Galaxy\storage\galaxy-2.0.db
PLEASE NOTE this will require you to scan/import your locally installed games, Galaxy will take a while to load everything at next launch, blablabla. Basically your Galaxy gets partial amnesia from this, but it's fine and faster than reinstalling.
Some more interesting notes:
Digging in logs a little,
does anyone else see anything about failing to load product configuration for product ID 1440151285 ?
If that sounds a bit meaningless for you, open up your last GalaxyClient.log file in C:\ProgramData\GOG.com\Galaxy\logs and ctrl-f something like "Critical exception during ClientCore task LoadProductsTask: Error Message"
If everyone is seeing the same productID, that would be pretty interesting and probably relevant information to get this humdinger fixed faster.
@ Whatever goglins are most likely reading this thread - 1440151285 is some internal ID I guess. Maybe try just installing whatever that game/DLC is for a repro? Error is consistently that ID for me and the ProductConfiguration for it is in fact missing
Saved me a fresh install so thank you very much for that.
Also wish that this forum was easier and faster to reach.
Even if gog doesnt fix everything at least community solutions should be easy and fast to reach.