Firstly, please make sure that you are using the latest version of your preferred browser.
Then please try clearing your browser's cache and cookie files. After the cache is cleared, I strongly suggest performing a full reload of the site (Ctrl-R), then logging out and back in.
It is also possible that some plugin or add-on is interfering, so please try using your browser in incognito mode. In Google Chrome press CTRL SHIFT N, while Google Chrome window is in focus.
If the above didn't help please try using a different browser.
Please also check if your antivirus or firewall software is not interfering - ideally by adding gog.com to its whitelist/trusted list.