Im not sure I fully visualize how your roof was constructed and insulated, but here is what I read. When you look at your ceiling you see an exposed 1x12? (could it be 2) rafter spaced at 24 inches with a V-groove wood ceiling exposed between the rafters. Above the V-groove you laid 2x4 barges perpendicular to the rafters and placed foam insulation panels. The metal roof is attached to the 2x4s without any ventilation gap.
This arrangement does not allow any moisture that penetrates the ceiling and insulation to be ventilated and it rapidly condenses on the cold metal roof. It runs downslope to the first 2x4 where it accumulates and drips past the insulation and through the ceiling. The results seem predictible.
This roof needs ventilation from soffit vents to a ridge vent to carry away moisture before it can accumulate and condense. A vapor barrier behind the ceiling and under the insulation would also help. The recommendation would be to install the new roof on flat 2x4s that run on 2-foot centers from the soffit to the ridge. The air gap this creates would have a natural convection that sweeps air from the bottom to the top of the roof. Whether the roof deck is plywood, OSB overlaid with felt and conventional roofing, or if it was simply replaced with a metal roof wont matter as long as ventilation is provided.
Post back if I misunderstood anything, or if you have more questions.
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