Uniques Disappear After attacking them

Hello Guys

can anyone tell me please why uniques at Holy water temple Disappear while players attacking them ?

they spwan and walking around when players start attacking them and got 30 - 40 % of HP , uniques Disappear

any idea why thats happen ?

Thanks alot

no reason to Disappear in HWT but maybe you decrease Area in HWT. but i don't think