Before you update your company files, let's make sure these files are not damaged or corrupted, Thomas.
We can do the Verify and Rebuild Data process to get rid of any data-integrity issues on your company file. You can use this article for reference: Verify and Rebuild Data in QuickBooks Desktop.
After that, you can try converting your files to QuickBooks Pro 2019 again. You might also want to browse these articles for additional information about the process:
I'l be right here if you need more help with this.
