That is a container for adding water softener salt.
Here is a service manual https://www.buyspares.co.uk/images/mediator/1513/service%20maunal%20-%20cdwtt13.pdf
And here is a user manual of a similar model showing how to fill the container
https://retail.mideasouthafrica.com/wp-content/uploads/2020/12/WQP6-3602F-MANUAL.pdf
So there should be water in there and it should be circulating but if there is a clogged hose it might be stagnant and allow all kinds of smelly bacteria to grow.