There are three things that will mess with everyone's masking-release experience: heat, acetone, type of plastic.
The problem with sign vinyl, is that almost all of it has acrylic-based adhesive that is susceptible to heat. Letting your disc return to room temp is always the best idea.
Acrylic adhesive is also susceptible to the ketone-group solvents like acetone, so, if you are using the acetone/water bath method, this could soften your adhesive and cause separation from the vinyl--no matter what temp.
Higher density plastics (Champ, Opto, Evo, SRP, Star, Goldline, Supreme) are going to give you a better release overall. More permeable plastics (DX, S, Pro, Pro-D, Power, "Soft") are going to give you the most problems, especially after acetone exposure.
The problem is that sign vinyl may be easy to acquire, comes in handy sheets, and is fairly cheap, it was never intended to be used as a masking. If you are wanting to dye discs on a regular basis and want pro results that work every time on every disc, the best remedy is to use a more high-performance tape that has a silicone-based adhesive. It's more spendy and you have to get it from industrial supply places like McMaster-Carr or Grainger, but it is truly superior in every way. Solvent and heat resistant, it makes a razor-sharp line and peels off cleanly and easily.