DIAGNOSIS The internal spray head is almost certainly clogged with mineral scale or coffee oils, preventing proper saturation of the grounds.
FIX Run an immediate descaling cycle, then a cleaning cycle. Fill the reservoir with a 50/50 mix of white vinegar and water. Place a large carafe under the brew head. Select SETTINGS > CLEAN > DESCALING and start the cycle. Let the entire reservoir run through. After it finishes, run two full reservoirs of clean water through using the same DESCALING cycle to rinse.
IF THAT DIDN'T WORK Check the physical spray head inside the brew basket area. Remove the brew basket and look up. Use a toothpick to gently clear any visible debris from the small holes in the black plastic spray head. Do not use anything metal.
HEADS UP Weak coffee can also be caused by using the wrong paper filters for the Single-Serve side. For the paper filter adapter, you must use the smaller #2 cone filters, not the larger #4 size. The wrong filter blocks water flow.