The first time I came across a discussion of this in SD, I sent (IIRC) a message suggesting that the term for this shouldn’t be (lethologica being excepted) a single word, but a phrase, amnemonic nondiction. Amnemonic because your memory is momentarily failing, and nondiction because you can’t choose the word you otherwise would.
But nobody responded. (sniff)
Probably nobody will this time, either.
I can’t think of the word I’d use to describe such people, but when I do … boy, are you gonna be in trouble!
I nominate apicolingualism as the name for the phenomenon, and a person who suffers from it would be an apicolingualist, from the Latin apex linguae, “tip of the tongue.” Apex linguae is also the anatomical term for the tip of the tongue, though rarely used. There is also a word “apical” in phonetics that refers to a sound made using the tip of the tongue.
A person who studies the phenomenon would be an apicolinguist, the study of the phenomenon would be apicolinguistics.
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“Aphasia” is perfectly good for nonce use by laymen, but it has a more precise meaning in scientific use. God knows it’s not the only word of which that is true.