Can you post a photo? Wilting of new plants can be caused by a number of issues.....transplant shock, lack of water, too much water or possibly a disease issue. But we can't tell without some visuals :-))

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The photos do help. I would suggest that during the planting the dark-leafed stems were damaged some how since the other leaves and stems look fine. Just cut the wilting stems off. Your plant will send out new stems.

Be careful to check moisture levels before watering by sticking your finger deeply into the soil so you don't over water or under water.

That would be my thought as well - stem damage. It can happen very easily when repotting and without you necessarily noticing. Until you see the wilting and die back.

But my question is, how is possible to take 2 months to show signs of damage?? Like the OP, I had a plant that was seemingly thriving, and then not at all.

What is on top of the soil in the Pot ? It looks like wood chips. I've never seen that before.

I often mulch the top of pots, though I don't grow clematis in pots and I use compost so that it blends in better. All my in-ground clematis are mulched with wood shavings to help keep moisture levels even, though I tend to pull it back a couple of inches from stems.

I 'mulch' my in-ground Clematis with stones. My mobile home property is covered with stones in the front and on one side of my property. I will also use stones in all of my 13 pots of Clematis in November/December after the ground freezes and I prepare to over-winterize them.