Home Bargains sell a washing machine cleaner. Empty crystals in and run empty on an over 60 degree cycle. Cured the problem with mine. Other brands are available lol.
Never used to be a problem in the days of top loaders and boil washes and clothes that were made to expect them. Now-a-days the moulds & bugs get an easy existence of it.
I use washing soda in with washing powder in the 60 degree wash .It softens the water as we live in a really hard water area and keeps the machine clean .
The only time I ever had a smelly machine was by using those liquid tab things .They gunged up me pipes and I had a terible stinky machine so I went back to powder.
I'm not a great believer in this 30 degree wash malarkey especially for towels and underwear and whites . You can't kill bacteria at low temps .I only use a low temp for clothes that need a gentle wash .