What is this peak at around 260 bp in our tapestation data?

[Vismundevil]

We prepared libraries for RNAseq (NEBNext® Ultra™ II Directional RNA Library Prep Kit for Illumina®), used 100ng total RNA as Input, and used NEBNext Poly(A) mRNA Magnetic Isolation Module and 12 rounds of PCR for library enrichment. Then we checked the libraries with a tapestation. Everything worked fine and we got the expected concentration measured by Qubit. Then we checked it on Tapestation.

Does anyone know what the peak at 266 might be? We find it in all four libraries that we did.