My favorite is non-mathematician Marjorie Rice challenging the proof of "No other pentagon tilings exist" with multiple new pentagon tilings. Schattschneider's [article][1] was the primary announcement of the results.


  [1]: https://www.maa.org/sites/default/files/pdf/upload_library/22/Allendoerfer/1979/0025570x.di021103.02p0247f.pdf