Recently interest rates have gone up.

Fixed-income securities, including mortgage funds, decrease in value when interest rates rise because existing mortgages with lower rates become less attractive compared to new, higher-yielding mortgages. The feedback from the document states:

"Fixed-income securities move in the opposite direction to market interest rates… Let’s assume you are the fund manager for a mortgage mutual fund, which has mortgages paying 5%. If mortgage rates suddenly increase to 6%, only the interest rates on newly negotiated mortgages would increase… The investor would not pay you par for a 5% rate. If you wished to sell the mortgages, then you would have to lower your price until the price paid—given the 5% fixed payments to be made—results in a return to the buyer of 6%, the ‘going rate’ on mortgages. In other words, the market value of your par value mortgages must fall."