It seems the recent SteamVR update was having problems with the size of my backrounds and would occasionally throw compositor errors. I don't have official word from Valve that this was actually a problem (I have a ticket in), but my own testing bore it out, so I took preemptive action.

I've reuploaded all of my backgrounds at a low enough resolution to avoid the crashes, but still give you the same detail as before. The updates should download automatically if you're subscribed to my backgrounds. You can also force the update by unsubscribing and resubscribing to the item.