"Failed to retrieve the size of the MP3 file for the track" and "Unable to download track" about bandcampdownloader

[Otiel]

I've experienced the same when downloading a lot of albums in a short period of time (be it in the same session of BandcampDownloader or not - restarting the application doesn't help). I suppose as well that it is a way for Bandcamp to prevent the kind of downloads we do, as you're not supposed to listen to hundreds of songs in a few seconds/minutes. The only thing I can tell you is wait between downloads.

But that shouldn't affect only specific songs, try again by downloading only the regarded album.

Replacing http:// by https:// in your album urls shouldn't change anything, as the program is using the http protocol anyway to download tracks.

[NeonLightning]

could this be fixed by adding an option to add a delay between track downloads?

[Otiel]

An exponential back-off has been implemented since this issue was closed. Did you try playing with these settings?