This has been reported before in 2020, but seems to still be happening.
Upon launching a game from the website, I frequently run into the “Same account launched from different device. Leave the experience on the other device and try again. (Error Code: 264)” error. This seems to only happen when utilizing the browser version of the platform, and sometimes I am forced into utilizing the Roblox app to join a game simply because it will not let me launch one from the website itself.
My system: Windows 11 Pro, 48GB Ram, AMD Ryzen 5 5600X @ 3.7Ghz, GTX 1660 6GB
Expected behavior
When click play, or join on a users profile I expect the game to launch as normal and allow me to play it.