Hello - yes, once a month every month I would (write it on your calendar) .. especially if most of the time you wash garments at 40c or under - some washing machines have a 'Auto-Clean' was programme cycle (I dont know if your particular model has) , but it will say in the instructions. It will fill up the drum with some water and heat it up to 90/95'c and then 'swish' the water around the drum very quickly as to 'scrub' the old gunky left behind undisolved detergent and grease and then at the end rinse it out. If you do a lot of low temperature washes have a try of adding some Dettol Laundry cleanser liquid to the wash cycle which will kill germs at under 40'c (allegedly) if you can get it where you live or something similar. - Dont forget to leave the door ajar after the wash and at all times if you can, it allows air to get into the drum and dry it out rather than leave it condensated and damp (which can lead to damp smell) and wipe the grey rubber door gasket dry after every wash and look for black mould on the grey door rubber gasket (sometimes if it already is bad with mould sometimes you cannot even get rid of it by cleaning and you have to have the rubber door gasket replaced or replace the machine altogether if the mould has really got in there and taken hold. Have you ever cleaned out the pump filter on your washing machine? - on most washing machines the pump filter is behind a door or facia at the bottom of the machine (the instruction booklet will say how to) sometimes if they are not cleaned they , over time, get full of gunk of undisolved washing liquid / conditioner, hair, fluff, coins and buttons, and sometimes if the filter is dirty and need cleaning a 'damp' smell can emulate from the machine, Come up from the pump filter and the smell then can come out through the drum and soap drawer. Talking of soap drawer do you take that out regularly and clean it ? most soap drawers can be removed totally from the washing machine by pushing a clip down at the rear of the soap drawer same time while pulling out the soap drawer. Clean all the undisolved washing powder and soap liquid and conditioner off the drawer insides and at the bottom of the soap drawer and rinse it well and then dry it totally before putting it back in place. Again a 'yucky' soap drawer attracts mould and can give off a pungent damp smell. - Good luck , I am sure you will eradicate it or make it smell better in the end if you do all of that .. well I hope anyway.
EDIT: I have sourced the Instruction Manual for your washing machine here: https://www.manualslib.com/manual/46003/Electrolux-Ewg-12440-W.html?page=3#manual