Guild Wars 2

On my warrior who has aslways the same set equipped I keep getting different numbers of health. Please note – I do not swap weapons or anything (plus all my weapons have same stats).
It can be 20,902; 21,102 and today it’s 20,102. Not sure about 20,702 and 20,802. Might have forgotten some other options as well.
What sorcery is this?!
I remind you -gear and locations are the same every time. No vitality buffs applied, n-o-t-h-i-n-g is changed in character’s setup.

World bonus from WvW.

Aye, found it.
“Robust”.
Thanks!