I encounter the same issue in WvW (never in PvE).
Everything goes well for a moment and suddenly for no reason I cannot see any other PC even if I still can select/target them though sometimes they suddenly appear in front of me. Very annoying and frustrating. I have been killed two times this morning this way and it got me mad.
I have never encountered such a problem before this morning and the latest update.
I play on a GTX560Ti with latest NVidia drivers if it can help.
Thank you.