I’ve had this happen on Phals with poor root health. It might be worth checking out what’s going on below the surface. Especially if you’ve had it awhile and its former keeper didn’t do one, repotting into fresh media may be beneficial.
If you do decide to repot, be very conservative when cutting roots (it’s better to leave dead ones on than accidentally cut live ones off), and don’t prophylacticly spray the roots with hydrogen peroxide or other chemicals.