Oxidation of Sodium Hydroxide in Ethanol?
[Answer based on comments from @KemonoChen, @IvanNeretin and @NilayGhosh. Thanks for your input :D]


  In the presence of alkali (or acid, for that matter) aldehyde will
  turn against itself, creating all matters of ugly polycondensate
  products. See Aldol
  condensation and
  note that it ends up in another aldehyde, so the process can and will
  be repeated


So yes it can happen.

And is is most likely ethanol oxidation to an aldehyde, which has (aldol) condensed into an 'ugly polycondensate'

It may also be Sodium Alkoxide, which is known to turn brown.