I had this problem a couple days ago and it’s kind of odd what the source was: the endpoint was having some issue and in need of a restart. I had never had issues with my network being slow before, though it sometimes would take time for a track to start playing while the NAS is spinning up. Room was patiently waiting for that without giving me this message.
After restarting literally everything involved on the source side (NUC, NAS, access point), I still got this message. So I restarted the last thing that I could, which was the end point (a Pi running DietPi), and voila, everything worked great again!
It’s weird that Room complains about the file loading slowly when it should know that the end point is pushing back and slowing things down/not able to deal with the data. It would make diagnosing and fixing the problem much easier if the message reflected what was going on. I even wonder if some of the issues people are having with TIDAL are caused by the end points, but the message is misleading there as well.