Update on this one:

when weather on 25/02 was bad in morning at FRA, and all but one of the BRU flights later that day were cancelled in one go, so no compensation as considered a 'valid' decision by LH (afternoon cleared up so for most pax impact of morning distruptions not overly bad, only BRU and a little bit AMS re-bookings were heavily impacted, plus a little bit of a reduced schedule intra-Germany).

So be it, leaves me wondering a bit as to why BRU flights are easy victim for this kind of decisions as friends tell me this happened to them as well sometimes (well ... guess I actually know: short flight, non-important people )). Will teach me to try & avoid connections in FRA, and I like MUC and ZRH better anyway