The same issue occurs for me and it is the strangest and is kind of a concerning issue. I am on a custom built PC operating on Windows 10. Latest version of Chrome as a browser. It appears that simply unplugging and plugging my HDMI monitor connection brings back my display however it is by no means a solution. I shouldn't have to manually reach around and rewire my system due to a crash from what I have determined to be the web player.
I have had it happen at 5 different times of the day, over two days, and everytime it was due to either opening the webplayer directly from Google or following a link to a playlist. As soon as the App opens, 3 seconds later my monitor disconnects from my system.
Acer monitor behaves as if cable was disconnected/signal was lost, 100% of the time. ASUS monitor does the same, so far 50% of the time. So far, after a short delay, the Acer monitor has recovered once. The ASUS monitor has recovered each time. Primary monitor (laptop's built-in) works fine.
Close the browser tab with the Spotify web player. Everything is awesome again.
IE doesn't support the player
Edge seems to work, as does Firefox. (FF is intentionally very out-of-date, so it's not a good test.)
Seems all Chrome so far.
I have shot a brief video of this happening, but would prefer to send it privately.
I have the same problem, with a 4 monitor setup. Regardless of which window the browser opens on, my central (asus) monitor will appear to disconnect and then reconnect. This only happens when the webpage loads, and lasts for after a few seconds. It is very frustrating. Anyone found a solution yet?
Edit: The same probelm occurs when closing the webpage :(