Maybe, at rest and with time, the solution stratifies to the point that the bottom layer reaches saturation? See if vigorous stirring drives the the precipitate back into solution as the bottom layer mixes back in with the lighter layers.
A solution of 50% NaOH is not going to randomly precipitate -- or even stratify into different layers of concentration -- just by sitting around. That is honestly not going to happen. We're not making a saturated solution when we masterbatch at 50% NaOH. At 60 F (15 C), an NaOH solution is saturated at 52%.
If a 50% NaOH solution becomes sufficiently cold enough -- somewhere between 50 F (10 C) and 60 F (15 C) -- then the solubility of the NaOH drops and it may indeed precipitate. At 50 F (10 C) NaOH is saturated at only 32%. But that's not the situation the OP has described.
At 60 F and above, a white precipitate in a 50% NaOH solution is something other than NaOH. Sodium carbonate is the very likely candidate. Vigorous stirring won't make this precipitate go back into solution -- and that's yet another reason why it's not NaOH.