Thanks for the suggestions, Nicodem.
#3 is ruled out, the flask before extraction smelled very very much of almonds. I did this reaction in the past with different workup, just salting the benzaldehyde out of post-rxn liquid and it definitely gave results (together with bisulfite adduct forming)... maybe tried to bee too smart this time with the xylene...
#1 is an interesting one, could you say anything specific about it? Obviously, the bisulfite won't form while basic, but does too acidic hurt? I'm not sure about the actual acidity of aqueous phase... it contains damn sodium acetate buffer
What should the "optimal" pH bee?
#2 is dubious for the reasons you mentioned yourself. Do you have any hard data on the hydrolysis?
I guess under #4 goes the phase miscibility problem... Barium even suggested using PTC for these adducts,
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(Barium: "PTC for bisulfite-adducts", Methods Discourse)