Plaster around door falling off

We rent on the ground floor of a relatively new duplex complex; maybe 10 years old. There's been an issue with condensation, damp, and mould around the doors and windows since we moved in. The landlord told us when we moved in that this was an issue and to be careful about opening vents after showers and drying clothes indoors. We have been very careful about ventilation and once we get up we open all the vents and leave them open for the day, fully open the bathroom window after showers until the 'steam' is well gone, and open the external bedroom door every morning until we leave. We bought a dehumidifier for drying clothes and only dry them in the hallway with all the doors closed, the hallway is the only room without damp. However every morning without fail (even days when laundry hasn't been drying for four or five days and the dehumidifier has been on) condensation is running down the windows and metal frames. Mound was forming where the frames meet the plaster which we occasionally treat with mould spray.

Since the summer the plaster around the bedroom door (metal double door, think it's Munster Joinery) and bathroom window has been swelling. I thought it was the paint and let the landlord know but she didn't get back to me. Today a three inch strip of plaster fell off while I was wiping away the corner mould. Everything behind the paint is a rusty red colour and there is a recurring pattern, which makes me think the galvanised beading is totally rusted and would explain the swelling.



There is however a problem with the gutters, the downpipe isn't positioned over the drain, which itself is raised above the surrounding garden, the result of which is the concrete back garden flooding whenever it rains. I recently managed to redirect the flow to the drain but it's only temporary. I let the landlord know. I'm also suspicious that the gutter is blocked as well but I'll sort that if I can get my hands on a ladder. I'm wondering if this could be the cause of the swelling around the door.

Basically I want to have an idea of the cause before I tell the landlord about this, could it be lack of ventilation due to us (I don't think so cause windows are open every opportunity and dehumidifier on even when clothes aren't drying), us drying the clothes inside (I don't think it's this either cause the room we dry them in with the dehumidifier is perfect, and this was happening during the summer when we dried them outside), the mould spray having some kind of reaction with the plaster (I tested it on the wall behind a cupboard first so I don't think it's this) or the outside drainage issues. I'd be happy to fix it myself at my own expense but of course I need to let the landlord know.

Appreciate any opinions.