You need to recompute the concatenated files.
Please make sure that you have the following lines in the file process_concat.m:
If you don't: update Brainstorm again, something went wrong
Unless you are using the compiled version of Brainstorm?...
If you do: Please post a screen capture showing your file, including the blue tooltip that appears when you leave your mouse for a few seconds over the file (I'd need to know both the file name and the file path for the "spectrum" file).