This is not a priority bug, but the behavior is interesting.
The small SSD C: drive on my server filled up (the stupid backup tool that came with my NAS has saved 24 GB of log files).
I was playing music when this happened, and Roon did not respond to new requests to play music, it kept playing the same song. Whether I hit Play (replace the current queue) or Add Next in the queue, it ignored me. Those added songs did show up in the queue, but Roon kept playing the same track.
I went to the server, found the problem, deleted some of those backup logs, and Roon recovered and played the songs in the queue.
Clearly an edge case, lots of things misbehave if the system disk fills up. Just thought the behavior was funny.
(I do need a better backup tool…)