When I run profit and loss account by customer report, One category is showing COGS by customer but another category is merging all COGS in UNSPECIFIED ?

Let's take a look and determine why some of the transactions are showing under customer and some are unspecified, M-Siddi.

The Profit and Loss report by Customer will display your income, expenses, and net income by customer. Therefore, when you record transactions like invoices and expenses, ensure to select the customer's name in the transaction. 

I've added a screenshot where it points out the unspecified transaction:

After we've drilled down one of the transactions of the said not specified amount above, we find out that one of the line items doesn't have a customer. That is the reason why it has been grouped under the Not Specified column.
 

On the other hand, those transactions that have a customer are showing on the COGs by customer column.

To prevent the unspecified option from displaying on the report, make sure to provide a customer when entering transactions. 

You can track Profit and Loss by Customer without using class or location tracking function. To learn more, go through this article for more information: How Can I Track Profit And Loss By Customer?

Moreover, you may also want to use different reports and projections to get a clear look at your current and future business finances. Use this article article for future reference: Track Your Cash Flow In QuickBooks Online.

Please let me know if you have any other concerns when running reports. The Community is always here to make sure everything is covered. Have a great day!