Alright so i'll keep the lenght at 2 sec. As the overlaps are not possible I set it to 0 % ? Or just leave it as it is ?
If you set an estimator window => duration of the epochs: there is only one window estimated per file, the overlap parameter is not used. Leave it to 50% so that you don't forget to change it back later.
The function bst_psd is called once for each epoch, and the results are averaged together because you selected the option "Output: Save average PSD values".
If you want to understand better what is happening: put a breakpoint at the beginning of function bst_psd.m, run the computation and when the debugger stops explore the contents of the variables, and follow the execution step by step.
here is the .mat file for the welch
I could download your files and both can be opened in various ways, on various Matlab versions including 2018b, both on Windows 10 and Ubuntu 16. No errors, no warnings.
I suspect there is something wrong with your installation of Matlab. Either reinstall Matlab, install another version, use another computer, or report this bug to the Mathworks customer support.