This paper presents the influence of overly stiff rail fasteners, which are used to stabilize rails on a ballastless track structure, on the mechanism of the occurrence of defects in concrete baseplates. During the analysis, there was a series of field tests performed on a real track, the purpose of which was the assessment of the technical condition of the ballastless track, the assessment of concrete baseplate strength and the verification of the correctness of the rail attachment by means of a fastener. In addition, there was a series of supplementary laboratory tests performed which assessed the relationship between the anchor clamping force and the torque at the assembly stage (the first tightening of the anchors) as well as after the adjustment of the fastening rigidity (loosening and tightening the fastening anchors again). On the basis of the obtained results, a three‐dimensional numerical model of a section of the ballastless track structure was prepared with the use of adaptive solid finite elements. The performed numerical analysis reflecting the real work of a fastener in a track structure was used to identify the causes of defects in concrete baseplates in the analyzed ballastless track structure.