First as a nit, your �substrate� is probably NOT copper. It�s probably FR4 fiberglass/epoxy.
Substrate. Base Material. A supporting insulating material upon which parts, components, and elements are attached.
Second, enough of that, on to your issue � comments are: * �Dwell� [time above liquidous???] is none too long. We�re not experienced with no-lead, but we�d expect liquidous +35*C to be 5 to 10 sec. * That your solder is not sticking to the pad and is globbed on the lead indicates [1] the lead is solderable and the pad is not. And/or [2] the lead is much hotter than the pad.
In [1] above, you should be able to test the solderability of the pad. It�s possible that the imm Ag was plated over marginally unsolderable copper and over time, it became less solderable.
In [2] above, assess this by measuring the temperatures of your reflow temperature recipe at the discrepant pads.
reply »