I'm really not sure what the "preferred" moisture requirements for those Queen palms are and it's possible , looking at your location , and perhaps in heavy soil, this winters abundant moisture may be keeping the soil too wet for healthy roots, as well and cooler than average temperatures perhaps combined with winter wet are not to their liking . Most likely it was planted in drought conditions some years back and had gotten quite used to very dry soil over the years only to find it wet and chilly this winter compared to past winters? Only a guess mind you and perhaps the others survived , not having suffered from root rot where drainage is higher or better than the one pictured? I did live in LA for a number of winters so I know how cool those wetter winters can be compared to average highs and lows etc.