for your first question, are you using single or double precision for your simulation? You can find out by looking at the very top of your Fluent window and looking for "dp" (double precision). If you're running on single precision, it may affect the precision of the data that you are writing to file.
Regarding your second question, is it possible that at time step 24, your velocity cg_vel is exactly zero? i.e. angular_freq*time = pi/2?
I hope this helps!