Profit & Loss Report not showing any income
The original poster says, "I opened up the Profit & Loss Details chart (under Business) and observed there wasn't income recorded for months where income was deposited." [Note: the community discussion Subject is incorrect; the discussion is not about the P&L "report": it is about the P&L "chart" on the Quicken Business tab.]
Two considerations affect business income from invoices.
Consideration one: Business income from Customer invoices is determined by the Category assigned to the invoice item. The invoice item Category must be designated an "income" category and that category must have a Schedule C tax line item assigned - either in the Category List or individually in the invoice itself.
Consideration two: "when" business income is recognized is controlled by the "basis" selected. When the "Accrual basis" is used, income is recognized when the invoice is issued. When the "Cash basis" is used, income is recognized when the invoice is paid. One corollary to consideration two is that the only time the payment of an invoice has any affect on income is when the "cash basis" is used; and then the only affect of a payment is to determine the date that the income is recognized. Invoice payment transactions are NOT themselves, income; they're just transfers from the invoice account to the payment deposit account (typically a checking account).
The default "basis" can be set for a Quicken file at: Edit > Preferences > Reports and Graphs. When the "Cash basis where applicable" box is un-checked, the Accrual basis will be used (when "basis" is applicable). The "basis" for any report where basis is applicable can be set on the Advanced tab of the report Customize dialog (overriding the global file "basis" for that report).
The Quicken employee posting in the above community discussion is not helping.
For example: you should not edit the invoice payment transaction in its Quicken deposit account to use an income category. That's not only not necessary, it will cause the payment to no longer be applied to the invoice (as one poster in the discussion has discovered). And you do not want to create a new (additional) deposit transaction in the Quicken payment deposit account, since that will overstated the balance in the deposit account.
[I do not see any "basis" problem in Q2020 Home, Business and Rental Property R31.12; and my R31.12 Business Profit/Loss Chart appears to be correct (and properly reports different results when I switch from "accrual basis" to "cash basis").]