Exact same problem here!

I've got the exact same problem, with the same negative number for greatest damage dealt, but with a bit different conditions.

Place of accurence: Valley of the Kings
Active skills when this occured: 16pt Wolves, 1pt Nymph, 1pt Heart of Oak, 1pt Trance of Empathy.

I think this occured when one of my pets hit an enemy after activating Trance of Empathy, because when I was running with pets for a while without using ToE, I didn't get this bug. I remembered to activate this skill only after some time and that's when the bug occured (might not be the first hit, but it was soon after using ToE).

Edit: This also might have occured when I accidentally hit an enemy myself, but only after activating ToE, because I'm not sure if pet damage even registers for Greatest Damage Dealt statistic.

This bug must have been introduced by Ragnarök. The new character I started for Ragnarök has "greatest damage dealt" at 0 (or negative 2 billion), as does one of my old characters that I've played for a few minutes, and killed monstesr with, since Ragnarök. Checked my other old characters, which haven't killed any monsters since the new expansion came, and they all have legit "greatest damage dealt" stats.

I've read that the bug occurs with retaliation damage. It's a very common bug that needs to be fixed by the devs.

The bug seems to be caused by retaliation damage yes, most commonly seen with dream mastery's trance of empathy or using shields with reflected damage, from what I've been able to gather. My guess is that there's a bug in the calculation of it resulting in negative retaliation damage being dealt, confusing the greatest damage dealt property here. But only the devs will know for sure :)

I also have this annoying bug
Greatest damage "-2147483648" - this same stupid number

Same here, love the game, please fix !

C'mon guys, 2.5 months have passed since reported.

Fix this bug please

Fixed