Might need water. Most bamboo really doesn't like wet feet, but in a drought, mine can start looking like that, but I haven't seen much of it with all the rain we had. Still, I see stuff in different stages of dying, so I might challenge it with some brief waterings. The clump looks pretty healthy. It looks like there's a new shoot. I think I'd cut it out so new browning is more obvious from the start and note the browning starts with leave tips. Mine really like a handful of lawn fertilizer from time to time, used with discretion. Not that I think that's the problem here.