I'm not 100% clear on your parts or assembly but it sounds simply like you have coating solution that was trapped and has leached out. This is common but it often ties back to the coating supplier not using an adequate rinse process after conversion coating. Your last sentence is not at all true. I've been dealing hands-on with plating & coating of parts for 35+ years. The bake cycle does not remove coating. However, depending on the process used and if not done properly or if part geometry is not favorable, the coating process will not provide coating in some areas and will often leach coating solution residue over time.

- EM