Identifying Chrysis ignita group species is challenging, they often look much alike and characters used to differentiate species are very subtle. Here, I've made an effort to compare C. vanlithi to more "typical" members of the ignita group:
Finally figured this one out: it's Chrysis vanlithi (Linsenmaier, 1959), a species known from a select few localities in the Netherlands (no recent records) and as far as I'm aware not yet reported from Belgium.