Does Laezel have Great Weapon Fighting style? That would add complexity to how it's calculated, and I don't know what the order of operations would be.
That being said, 21 out of 24 damage is very, very high. You can't have any damage d6s at 1 or 2, and at most a single 1d6 on a 3 (with all three other damage d6s being a 6 in that case, 6+6+6+3=21)
The tool tip is confusing at best, and maybe "wrong", perhaps by having old values there not relevant to this roll, but this particular damage roll seems fine to me since it's such a high result, it seems unlikely without some damage rerolls working correctly.
But I can't make any sense of the tooltip - why does it have 13 values? I only can make sense of 10 values - 4 damage dice rolled twice makes 8, and rerolling 1s would make 10. And there are d6s on a 6 with reroll symbols, or cross out lines, which also makes no sense to me.
I think it took two 6s, a 5, and a 4 - that would make 21, out of values you rolled. Why those ones? I have no idea lol
Maybe you could send this to support, and just ask them to explain the tooltip