Poly mounts have a major design flaw, the opposing sides within the poly run up/down.
I've posted this before with pics.
This works ok when pulling on the mount from the top/bottom of the mount, but that's not reality.
Each side of the mount will slide past the other, causing the engine to twist on both mounts, and eventually sag on both sides.
I have a factory big block a-body, with a tunnel ram, and the driver's side mount is forward, and slightly different. The passenger side, same as a b-body mount, would sag and the engine would end up against the hood.
After much back and forth with Schumacher, proving both mounts were separating inside, had little visual outward damage except that they looked a little 'melted,' installing heat shields per their request, although the driver's side mount is miles from a header, multiple new mounts, taking measurements before and after, cutting them apart, them insisting I have Schumacher headers, which I did, they gave up stating they've never had this problem before. Imo, no one ever noticed.
I ended up drilling through both mounts and running a bolt through them. It worked for a few years, but now the passenger side is against the hood again and I'm putting rubber back in with a bolt through them, to both act as a torque strap on the driver's side, and to keep the mounts together.
I have no ill feelings towards Schumacher, they did everything they could, and during this process I wasn't convinced they manufactured the mounts anyway. Even with a pic of a mount cut in half on their website, they couldn't describe how they were put together and couldn't make a set with the internal 'locks' turned the other way.
In retrospect, that wouldn't really help, as there would eventually be internal metal to metal contact.
A friend with a b-body didn't believe me, until I showed him how his mounts looked 'melted' like my passenger mount, and had clearly slid internally.