I too have experienced problems. I upgraded about a week and half ago. After upgrading version, I opened up the company file as usual and for the last week and half going along thinking everything was fine after a slight bug with not being able to email invoice. Today, I check in on the chart of accounts and found a couple of the account totals were way off! After, I was able to restore my last 2016 back up in my 2016 copy of QuickBooks desktop pro and compare with it version after the 2018 upgrade, I confirmed that was the most likely cause for this discrepancy. Thankfully, going the route of restoring backup with the last 2016 copy and having it upgrade that copy worked. Account totals are good. Unfortunately, I will have to redo some work, but at least the starting point is fixed.