“Export multiple” of album results in some tracks exporting as only 1KB.

I am using Windows 10 and Audacity 2.3.3.
I have recorded an album with first track of 5 minutes and track #5 of 2½ minutes (11 tracks total) but Export Multiple in either WAV or MP3 results in these 2 tracks exporting as only 1KB with only the label and no music data. On another recording I’ve discovered that a 1½minute track has exported as 151KB and it plays for about 7 seconds.
I was originally using version 2.3.2 but have downloaded the latest version and tested it only to find the same result.
I initially made this discovery by adding these albums to iTunes only to find that these tracks were missing altogether in iTunes.
I’m hoping someone may have an answer to this and that I won’t have to rerecord these albums and start afresh.

Are you using “point labels” or “region labels”?
How many files should there be (how many labels in the project), and how many files are actually exported?
(If you don’t still have the project file, then it’s unlikely that we will be able to get enough information to be able to work out what caused the problem).