I also had a flame that died on me randomly after 3 months...
I had ask my LFS
to special order that one for me. Owner was very reluctant saying that he had very bad Flames experiences with a high death toll and stopped stocking them. He was right
This always seemed weird to me as a lot of info out there recommend the Flame as a beginner fish
I now have a keyhole angel I recently got and it seems in top health eating everything I throw at it.
Sorry for your angel troubles