I downloaded the latest update to Gwent a few days ago, and ever since I've tried to start the game I get the same prompt telling me: ''Could not connect. User is not signed in'' allthough I indeed am logged in the GOG client and tried the website too.
I tried searching this problem up, but I found very little information how to really solve it. Any help?

This post of yours is a year old. I did not update the game I just downloaded it today. I found out about this game by finding it on the PS4 a few days ago and loved it a lot. I cannot seem to get into the game after downloading it and installing it on my PC either. It keeps telling me that the login information is incorrect. I'd like to know if you were able to fix this issue or not.

Maybe GOG's sister site, FCKDRM.com, can offer some clarity. I looked again just now to see what they say about this whole signing-in business for accessing games. Seems to me that the root problem here is the game being DRMed.

"Digital Rights Management, DRM, is a really broad term for tech that controls how, and when, digital content can be used – like your games, music, video, or books.

Games with DRM include a layer of software or code on top of what's needed to just play the game. Nowadays DRM will send your information to an online server, it could run checks to see if you touched any files, or outright refuse access unless you're logged in somewhere.
...
Why should you care about DRM?
Because there is a killswitch built into your games. Sure, DRM might not affect you right now, but corporations hold the key and they'll only let you in as long as you can repeatedly prove ownership. As long as you're connected to the internet. As long as their DRM works without fault. As long they're still around.

Backup, copy, use anywhere
No one else gets a say in how you store and access your media. You bought it, you own it.


Access offline
Don't rely on your internet connection. If not on principle, then for stability and convenience.


Keep your consumer rights
Don’t hand your rights over to corporations that wouldn't trust you. Some relationships are based on trust, others on control and suspicion.


Support digital preservation
By choosing the right sources, you know that the content you bought will remain with you – no matter when it was created or for what hardware.


Lose all access, just like that
Online ownership checks can, and do, fail. Scheduled downtime, technical issues, and corporations shutting down are just everyday facts of life."

You should probably contact support then..But if it tells you that the login information is incorrect then you should try and reset your password..