the hot cycle starts to dissolve soap sludge from your machine.
If you have not given it enough hot cycles for the water to stay clear and non-foamy, you are putting your washing into dissolved sludge.
the first hot wash often makes it smell worse, because you are starting to loosen it, but have not yet washed it away.
cool washes do tend to cause sludge build-up. If you have white cottons, such as towels, and give them a hot wash once a week or so, with very little powder, it will tend to clean out that sludge that builds up from your cool washes. If you add half a cup of washing soda it seems to dissolve the soap sludge faster. In my own house I have a water softener which is much better at dissolving soap, and less product is needed anyway.
Adding extra soap is one thing you don't need to do when trying to clean soap residue out.
A hot wash will also kill the existing mould spores on the washing, so they start fresher.
It's not the powder or liquid that causes the sludge, it's the low temperatures.
If you use a dosing ball, or put the powders scoop straight through the door rather than into the drawer, it will dissolve faster and not lurk in the drawer or chute (you can see laundrettes are terrible for that)