damp wall puzzle

[Alan16]

About a year ago I noticed the hall wall was a bit damp-flank wall with outside rainwater drain opposite damp. I took up a floorboard and found it was wet on the ground near the wall and eventually found that the cement surround of the drain was cracked and leaking water downwards.
I fixed that by recementing it and the wet dried up and all was well.
Recently however, I've found about one meter up and about two meters length of the same wall is damp - worse than before. I've taken up floorboards and found it dry below.
A damp company says the damp proof course has failed and I need a chemical damp proof course.
Why would it have failed? and could there be another cause?
As far as I can see, water isn't leaking from the drain.
Advice much appreciated.

 

[foxhole]

A damp company says the damp proof course has failed and I need a chemical damp proof course.

They always say that, otherwise they are out of a job.
There is another cause.
Check the downpipe again they can crack wall side and this can be difficult to spot, gutters could be leaking , loose or blocked, any external pics, both close and distance.?

 

[Alan16]

I can't see where the water can be getting in from the outside now the drain is repaired, so I have tried, possibly in an amateurish way, removing a section of the wet plaster at the bottom of the wall and replastering it.
The replastered bit is about five days old now and a damp meter reading shows it is more or less normal compared with the damp reading for the surrounding plaster. I realise that salts in the wall will contaminate the new section of plaster I also understand that the damp meter reading may be unreliable, but apart from the wallpaper slightly peeling off ,high damp meter reading for the old plaster and the old plaster being blown, there is no other sign of damp

 

[foxhole]

The damp meter is for timber , not walls, surface use only detects condensation not damp.