I have seen this kind of "failure" quite a bit recently.

In most instances, I have determined that improper assembly is typically the culprit.

Old fashioned chains had thick plates, with considerably more central pin bearing surface, that were more forgiving when utilizing a standard chain tool.

Modern chains typically have very thin sideplates that are much more sensitive to proper assembly. If you assemble the chain in the conventional manner, and end up creating a larger than factory specified gap between the plates and the central (inside) link, under heavy pressure, the chains quite simply pull apart.

Improper assembly can also shear a crescent shaped sliver of sideplate (via pin push) that will guarantee failure eventually.

The cure? Carefully assemble the chain with a conventional chain tool, then measure the plate span at the connection, or induce a "stiff link" condition, and institute local deflection manually to open it up, or the best yet, get a chain that has a "master link" system (Wipperman etc.) that will not allow operator error in installation. There is a reason a lot of chain manufacturers have this feature.

BTW, if you did use a "master link" style, and did not Malachi anything else...............the chain was too tight.