QB Issue Resolution:

If you are willing to send to Intuit the company file and an iif file (that hasn’t been imported yet – like the backup made before you import) then we can have a look at it.

Resolution for Issue 'IIF Import dropping last transaction.Why is that?' available: Yes (Solved).
Source: Intuit Community forum.

IIF Import dropping last transaction.Why is that?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Import
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Error Recovery for Import [Canada]
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