Twisted generalized Reed–Solomon (TGRS) codes are evaluation codes that include many MDS codes not equivalent to GRS, and their Schur squares can be much larger than those of same dimension GRS codes. Leveraging this, Beelen–Bossert–Puchinger–Rosenkilde (2018) proposed MDS Twisted Reed–Solomon (TRS) codes over Fq with ℓ  twists for McEliece, claiming resistance to Sidelnikov–Shestakov and Schur-product-based attacks. We show that the claimed resistance of TRS/TGRS to Schur-product-based attacks is false: a broad class, including TRS and TGRS, is distinguishable from random by computing the Schur square of suitable shortenings. Focusing on the single-twist case ℓ=1, which is most efficient for decryption, we derive a practical attack akin to the 2014 distinguisher-based attacks on RS-based systems by Couvreur, Gaborit, Gauthier-Umaña, Otmani, and Tillich. We analyze the success probability of the algorithm of the attack, yielding a provable break.