It is more likely to get help, if you provide a minimal example with a relevant subset of your data and a necessary portion of your code for plotting the data. Additionally, it might be helpful to know your operating system and Octave version. I see the problem, but at least I am not able to guess what went wrong in your case.
Octave 4.0.3 quite old (2016)  and many many improvements had happend since then. If it was possible, try to upgrade to the recent stable version 4.4.1 and check if the erroneous behavior is still present.