At one time a short alkaline bath was recommended by some companies as a post-fix treatment. Carbonate was recommended by Agfa for example. Metaborate has also been recommended. An alkaline pH means more swell, which can help speed washing. It could essentially undo the hardening action of alum hardener (in a typical hardening fixer), which is why the treatment was not recommended for alum-hardened prints. But this is a non-issue now (does anyone even use hardening fixers anymore?).
A sodium bicarbonate solution has a lower pH than carbonate or borates. The pH would likely be somewhere just above 8. Still alkaline but only mildly. And unless you give a thorough rinse before that, any residual acidic fixer might neutralize the weak bicarbonate alkalinity anyway. There was likely another reason for the bicarbonate recommendation. We'd have to get some chemist input. We know that even the properties of your tap water can have an effect on washing.
If you're using progressive trays of standing water, I might recommend short running water rinse between trays to get that "laminar layer" off before going into the next tray of fresh water.