There have been several reports of contaminated alcohols. Whether these alcohols are used as the solvent for the eosin or only as the dehydrant after staining does not seem to matter too much. They can cause serious deterioration of stain intensity. This is a relatively uncommon problem, but if you are certain that alkali from the blueing step is not the problem it would be worth while checking this out. Eosin is the sodium salt of eosinol.
Similar compounds exist for the other eosins as well.
It is quite simple to make, but can be purchased. It may be named eosin Y, spirit soluble . Make sure you do not confuse this with ethyl eosin which is also called by that name. They are two different compounds. Add concentrated hydrochloric acid to precipitate eosinol.