Very important - please look at this link: http://www.fieldtriptoolbox.org/faq/should_i_add_fieldtrip_with_all_subdirectories_to_my_matlab_path/
The issue with functions from /external replacing original MATLAB functions:
Use the following in your custom startup.m
addpath('Y:\Sources\fieldtrip-20190130'); % or other path to fieldtrip ft_defaults [ftver, ftpath] = ft_version; rmpath(fullfile(ftpath, 'external', 'signal')) rmpath(fullfile(ftpath, 'external', 'stats')) rmpath(fullfile(ftpath, 'external', 'images'))
… or just execute
https://github.com/dagdpz/test_FT/blob/master/test_FT_initialize.m on clean MATLAB path (i.e. without added FieldTrip)