Found the same Bug. Looks like it happens more with Tennogen skins because it worked fine on my Mesa Prime's default skin.
I hope they fix it soon because I love Mesa with Eclipse.
If you use Kullervo's Wrathful Advance with Gunblades it will often just ragdoll the enemies around and cause minimal damage.
Warframes tested: Limbo and Nezha
Gunblades tested: Stropha and Redeemer Prime
Some Mesa Prime Skins looks like are made from plaster when you toggle On the Prime Details and activate Mirage's Eclipse. I'm not sure if this also happens with other frames.