Thanks for reaching back out. What version of GitLab are you using on the newer instance? I did some digging and found this issue where a couple of others encountered the same problem - Gitlab Project import fails: sidekiq undefined method import_jid.
This comment on the issue provides a link to the import/export documentation on version history and compatibility. It looks like the import/export tool is only compatible between GitLab releases that share the same import/export versions, with the table in that doc detailing each GitLab release that changed the import/export version.
For example, GitLab
8.13.0 started utilizing import/export version
0.1.5 - this was changed in GitLab
8.17.0 when version
0.1.6 was released. This means that you can use the import/export tool between GitLab instances running versions
8.13.0 - 8.16.9, but trying to do so with GitLab
8.17.0+ will likely fail as the version of the import/export tool then changes.
So, if your newer instance is anything past GitLab release
8.16.9, then that is your issue. If you follow the upgrade path to a release that contains a compatible version of import/export for the newer instance, then you should no longer have any issues importing those projects.