How to re-analyze MP3 and fill in empty Codec,Bitrate, Length?

I let Mp3Tag scan my whole mp3 directory tree and display all the songs in the overview list.

It works fine for 99% of the songs.

However I found some MP3 songs where some important tags are unrecognized (=columns "Codec", "Bitrate, "Length" are empty).

The MP3 looks good. I can play it successfully in various audio players.
The meta header itself (ID3v1) exists and contain e.g. title and artist.

So why does MP3Tag not display codec, bitrate and length as for all the other songs?

I tried adding a blank at the end of the title and re-.save the meta header. But it didn't help.
Codec, bitrate, length remain empty.

So how can re-analyze the MP3 and fill in the columns ?

MP3tag only deals with the tags but not with the audio part and its parameters.
You would have to scan (and possibly repair) the files with the usually recommended utilities like mp3val, foobar2000 and/or mp3diags.