Hello there, mox. 

There are a few things we'll have to verify. First is the transactions affected account if it's correctly associated to account B. Also, the date range of the report if it includes all the transactions linked to account B. 

We can filter the report and see if the transactions are shown correctly. We can also double-click on the transaction if it needs to be changed. I'll show you how:

1. Go to Reports > Company & Financial > Profit & Loss Detail. 
2. Click the Customize Report button. 
3. Select the correct date range of the report. 
4. Click the Filter tab and click Account. 
5. From the Account drop-down, you can click Multiple accounts. 
6. Select only account A and B. 
7. Click OK to refresh the report. 

You can also use this reference to know more on how to customize reports. 

Let me know if you need more help. Take care always and keep safe as well!