I know kind of silly question, but could be your water vs. the salon's. If you have lots of minerals (hard water) it's almost impossible to use Deva products. I had the same issue (about $200 & 6 months waste) till I figured it out.
A great sub for Deva gels (IMO) is flaxseed gel, it's easily and cheaply made at home or Bottecelli Babe makes her own line (which folks rave about) available in Etsy.com.

Back on the CG wagon!
Hair Type: 2c/3a winter, low porosity, protein sensitive
(Cleanse w/Distilled water only)
Shampoo: Baking soda & brown sugar
Condish: Sauve Naturals green apple or aloe waterlily
Rinse: ACV
LI: Kinky Curly Knot Today
Styler: homemade flaxseed gel, topped w/KC Spiral Spritz
DT: veg. glycerin mixed w/conditioner
"Life's a garden. Dig it."