Class A: Paralyze, Slow
Class B: Acupuncture, Blind
Class C: Immobile, Sleep Chaos
Class D: Lower Defense/Resistance
Class E: Poison, Ignition
Class F: Tag, Imprison

Higher classes get cleared first
ex: Paralyze gets cleared first before Immobile, Acupuncture gets cleared first before Poison

When 2 debuffs are of the same class, the first one inflicted gets cleared first
ex: Slow is inflicted then Paralyze> Slow is cleared first, Ignition is inflicted before Poison> Ignition gets cleared first
In cases of Poison that is applied multiple times, the order it was inflicted is moved
ex: Poison is applied, then Ignition, then Poison again> Ignition gets cleared first

For a video tutorial that explains the Debuff removal order in action (made by Kenson): https://www.youtube.com/watch?v=BcfxDwSB-3k