Export/Import course but missing sub section

Hello everyone,
I have a problem with export/import course. After I import file tar into the new course, It is missing some of sub sections. I don’t know why it happens. Do we have any restrict for the name of section, sub section or unit?
https://drive.google.com/drive/folders/1QtHaKlRj_UBsomxtJS1YEc665-pDab2z

Kind regards,

I see that some sections are unpublished. Did you remember to publish the course before exporting it?