Migration Assistant Reports failed files, Prompts repair errors: No Documents transferred, High Sierra
It sounds like your Migration didn't work, even though you didn't get error messages saying so at the time.

I always use either Target Mode or an external disk when I use Migration Assistant. I also don't do the Migration until I've gotten the new computer completely up-to-date, etc. I create an extra "Admin" or other dummy account which I delete later.

I would reset the 2018 MBP, create a dummy account, do all the updates, and then when the system was running perfectly, then I'd start the Migration Assistant using the 2017 MBP in Target mode.

The other thing I do, because it didn't work correctly once when I did it a different way..... After selecting the source disk, MA will scan the source and identify the files, accounts, apps, etc. that need to be transferred. Since I was transferring everything, I didn't wait for it to calculate the sizes of all these different things, and just said "Go" or "Next" or whatever to get it started. That didn't work. So, now, I always wait for the scan of the source disk to complete. I wait to see the size of the Users folder, the size of the Apps folder, etc. before I start the Migration.

Good luck!