Newbie - Advice needed

Long time lurker, with the hopes of maybe learning something.

Location : Europe

Machine : Modern top load

Water : Hard

Air drying on rack

Products : Violeta - Color Washing Gel, Denk Mit - 3in1 Color Pods, Violeta Fabric Softener, additionally Vanish, Denk Mit color absorping sheets.

My problem is that my clothes - especially the light colores ones -, show stain spots after washing but not every single load of laundry. I read here that it could be the fabric softener or the washing gel being addes directly on the clothes/in the drum, but unfortunately using the fabric softener container is not evenly distributing anything that is added in there - the container unit is above the drum and when you close the doors of the drum only then you can close the door of the machine, so all the liquid stuff is pouring onto the outside of the drum and not gettinf inside on the clothes. Any advice of what i should or should not do?

Also, our machine has a rotten egg/swamp smell when we start the first load of laundry and the first couple gulps of water starts pouring into the bathtub - that's where the water is being lead instead of instantly into the pipes, lots of apartment building have been built this way. Once or twice a year we start an empty load on the highest temperature with a cleaning/decalcing powder or detergent.

Any advice is appreciated.