Terry Carscadden

I have 4 violin bows. My last one is new as of 3 mo. ago. It is a Cadenza* 302 carbon fiber bow. It weighs 60 gm. The others are 63, 65, and 67 gm. I have been playing the violin since age 10. I am 83 now but not good enough to go on the road! I play in a 15 piece orchestra. For the past 6 mo. I have found that all 4 bows are skidding on the "A" string only. I have used Pirastro Tonica strings for years. Two mo. ago I decided to try Pirastro Evah strings (4). The same thing is happening. I have tried less rosin, more resin. It is new Pirastro Oliv. Evah hard resin. I clean the strings properly. No significant difference. I am inclined to try other strings, e.g. Thomastik Vision or other. My luthier is as puzzled as I? I have not used any hair cleaner. I have gently cleaned the hair with a tooth brush then a few strokes of resin.
Any suggestions?
Thanks
Terry Carscadden MD
Sudbury Ontario
Canada