Thank you for your suggestion,
Indeed, printing out the eigenvalues is informative. In som of the calculations, I get outputs similar to this (last lines):
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 158 negative= 1 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 156 negative= 3 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 156 negative= 3 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
Hessian eigenvalues: positive= 157 negative= 2 zero= 0
So, two negative eigenvalues (although it has one at some iterations). However, I do get this from a subsequent freqency calc on the final geometry:
And visualization of the first mode looks very much like the correct ts.
Any suggestions on why the TS search gives two negative frequencies while the frequency calc only gives one?