Strutting off a truss web is not safe as no additional load can be applied to an engineered member, especially a truss web as it can not support additional deflection loads that it was not designed for.
Adding a under purlin, as the truss plates were falling off is not acceptable building practice for a truss roof that is failing. The truss web timbers are no longer adequately attached to or supporting the top chord.
Even the strut timbers used were undersized and the load points to the supporting wall frame not ideally located..
The solution for the above truss failure is best designed by an engineer, who will probably recommend gusset plates to be bolted to the members to strengthen and re align the truss web.