Blue Smart IP65 12/15 charger voltage incorrect (reads .5v high)

Hi I have checked thru the forums and have not seen this specific question.

I have an IP 65 blue smart charger which consistently senses a higher voltage than is reported by the shunt, which is right next to it. This causes the charging algorithms to under charge the batteries or as I saw in one post to jump from bulk to absorption or float sooner than it should. Question is am I missing something or is this just a bad device or firmware?
Appreciate any responses. This occurs whether I’m charging a lithium battery or a lead acid battery and multiple battery brands and versions.