https://replay.pokemonshowdown.com/gen7randombattle-849270900
Turn 28 - Camerupt puts 74.8% damage onto Aerodactyl-M using Stone Edge (non-crit) (damage calc backs this up). Aero-M roosts.
Turn 29 - Camerupt puts 32.8% damage onto Aerodactyl-M using Stone Edge (non-crit) (damage calc says min damage is 62%). Aero-M roosts to 93%.
Turn 30 - Camerupt puts 30.2% damage onto Aerodactyl-M using Stone Edge (non-crit) (damage calc is angry now)
I see no reason whatsoever that this would happen besides it being a bug.
Turn 28 - Camerupt puts 74.8% damage onto Aerodactyl-M using Stone Edge (non-crit) (damage calc backs this up). Aero-M roosts.
Turn 29 - Camerupt puts 32.8% damage onto Aerodactyl-M using Stone Edge (non-crit) (damage calc says min damage is 62%). Aero-M roosts to 93%.
Turn 30 - Camerupt puts 30.2% damage onto Aerodactyl-M using Stone Edge (non-crit) (damage calc is angry now)
I see no reason whatsoever that this would happen besides it being a bug.