We report bulk ultrasound measurements up to 77 T and down to 0.5 K of the field re-entrant superconducting phase of the unconventional superconductor UTe2. Clear bulk signatures of superconductivity are observed in the longitudinal c11 elastic mode for fields applied at a tilt angle of θb−c = 30[◦] from b-axis. We confirm an upper critical field of Hc2 ≈ 65 T at 0.5 K and bulk superconductivity which survives up to T ≈ 2 K for fields above the metamagnetic transition. The c11 mode has propagation and displacement vectors along the a-axis, and for fields applied at a tilt angle of θb−c = 30[◦], this mode is sensitive to the elasticity of the vortex lattice. The anomalies observed in c11 are in part reminiscent of superconducting vortices pinned to lattice defects. Nonetheless, an excess attenuation, with respect to the normal state, is observed throughout the entire superconducting phase, suggesting unusual vortex dynamics and pinning in the field re-entrant superconducting phase of UTe2.