Under current tax regulations, convertible notes (held by Fund A) are considered to be a type of OID (Original Issue Discount) instrument. Internal Revenue Code section 1272 requires holders of OID instruments to recognize interest income every year despite no interest being actually paid out. This requirement remains in effect whether the note holder uses the cash or the accrual method of accounting.
During the year, the convertible note held by Fund A converted into preferred shares. At the time of conversion, rather than paying cash for the interest accrued, the company issued additional shares to the fund. Because the fund recognized this increase in value, the tax code considers this taxable income and requires that it be passed through to the fund's investors.
Fund A invested into Company B which is a partnership/LLC. Under the tax code, partnerships/LLCs do not pay their own tax. The income or loss of the partnership/LLC is passed through to partners/members who recognize their portion of that income/loss on their own returns. Although Company B had a profit for the year, they have not made any distributions, but have instead reinvested that profit back into the company. Despite not receiving any cash, investors are still required to include that income in their individual tax returns.