Skill Render Issues (guard shield-5 and others) in WvW

Since a few weeks now, a lot of skill-effects, like guardians shield-5, sometimes also spellbreaker's elite and chronomancers gravity-well are not rendered in WvW fights.They get their combo-field line on the ground, but are otherwise simply not visible.Other skills, like scrapper's defense-field bubble are always rendered even in full blobs.

I noticed the problem with guardian's shield-5 even when no enemy is around (and we are ~25 in squad).In Teamspeak others also told me that in those moments the shield-5 was not visible to them.

Could this be a render-related bug?