The softener dispenser has a blockage, it's very common these days and some brands of softener are worse than others for causing it.
Pull the drawer completely out of the machine. Flip up the cover over the rear half of the softener dispensing compartment. Thoroughly clean out all of the (usually black or pink) goo which is causing the blockage.
The softener dispenses on a siphon principle, so there's a blind-ended upper tube moulded into the cover which fits over a lower tube. The lower tube is easier to clean out as you can pass pipe cleaner brushes or similar right through it, the upper tube will be trickier as you need to winkle out every bit of goo from just one end. The goo is a biofilm
, so if there are any traces left then it will rapidly re-grow.
Note that if you look carefully at the way the front panel of the drawer attaches to the main body of the drawer you can carefully unclip it. Once the front is removed you can safely put the rest of the drawer in a dishwasher to help kill off the remaining biofilm traces. I've done this thousands of times with Bosch/Siemens and AEG machines without any problems.
Clean the drawer regularly to prevent re-occurrence. You may also wish to consider switching to a wash powder brand with built-in conditioner, such as Bold: if you don't need to put conditioner into the dispenser, there's nothing for the biofilms to feed upon. They will feed on powder residues though so although you'll reduce the likelihood of getting further blockages you'll still need to clean the drawer (and the aperture it fits into) regularly to ensure that it never occurs again.
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