yeah, totally normal. One second they're hot on my heels trying to kill me... and then suddenly they've turned around and wandered off. Then they submerge and disappear. Just run around until they pop out and attack again.

The damage doesn't reset, so just keep setting them on fire with fire arrows, or lure them over surtling vents. My favorite abomination hunting area has like 8 surtling vents. It's where I go to farm coal quickly, the abominations are just the cherry on top.