Where are you located? And how has your winter and spring been? Clematis armandii 'Snowdrift' is vulnerable to cold winter weather, especially winds, which can damage foliage, resulting in the appearance you describe. Also very wet conditions in spring - like much of the country seems to have experienced this season - can develop some fungal issues that this vine is prone to.

Photos would help to clarify :-)

I have also had so many problems with my snowdrift. The new buds turned brown and the bottom of the stems are brown. I planted 4 plants last year, one totally turned brown last August so I pulled it out. Now the other 3 have some areas of brown on the tips of the leaves and the buds. I put in a new plant and it has brown spots on the new bright green growth.
Should I cut it down to the ground? Will it get new growth this year? I have them growing on an arbor and would like them to get back to being 10 feet tall.
Any advice on how to take care of this evergreen clematis would be greatly appreciated. I am so sad by their condition. I was so looking forward to the beautiful fragrant blossoms for Easter time.

Where are you located? Clematis armandii is not suitable for climates below zone 8 or sited where exposed to harsh winter winds even in that mild a zone.