The cause:
Some of the expenses fail to export because the number of receipts has exceeded the journal limit in e-conomic.
The solution:
In e-conomic, go to settings (Indstillinger), Finance (Regnskab), Journals (Kassekladder), Other options (Andre muligheder), and then Journal setup (Opsætning af kassekladde). Then go to Entry numbers (Bilagsnumre). Here you can increase the maximum number of receipts.