I know I’m not the first person to have this happen. Joined a warzone game, used a legendary exp req, after about 15 seconds, Halo 5 quit and took me to xbox home. I restarted H5, and it went through the whole splash intro/ msg of the day, etc. Sure enough, my legendary req was gone.
Dying immediately after spawn is one thing, tech glitches costing reqs is entirely another. These issues need to be addressed.