Guardian Angel 'Hero Stats Boost'

Hello Silvermistr.

I have noticed that just in front of the hero stats boost sometimes there is just a + sign (See S.King shot) and in some cases a + and a - (minus) (see Anatole shot where +- is in front of HP, PATK & MATK).

Reason for asking is that when I did some REFINE on Anatole ATK the HP hero stat for example went down from +- 236227505 to

+- 235911975, which is not what one wants to happen. Is there something I am doing incorrectly or something I need to change to make it to just a + and so increase HP, ATK instead of decrease?

Thank you