Thanks for replying.
Please treat all iD validation warnings with an air of caution. Many are dubious in accuracy. All warnings are ignorable.

In your example it doesn't issue the warning if it's connected to an adjacent highway.
Note if you create a platform from scratch iD doesn't ask you to add highway=footway.

Other poor warnings is adding public_transport tags to railway stations & platforms that aren't public transport such as tourist heritage lines.

Hi
When you add more railway=platforms mapped as polygons could you include the area=yes tag please.

Hi
There is no need to add any highway tags to railway platforms as their raison d'etre is to be walked on.

Hi
There is no need to add any highway tags to railway platforms as their raison d'etre is to be walked on.

way/897770582

...and are you sure it drosses the tracks?

Hi
way/888690610
What is this?
is it a road or platform?
If it's in a sidings yard it certainly isn't public transport.

Hi
There is no need to add any highway tags to railway platforms as their raison d'etre is to be walked on.

way/246778366

way/193979228/history
Hi
There is no need to add any highway tags to railway platforms as their raison d'etre is to be walked on.

Split residential areas around railways
way/142716923

Hi
There is no need to add any highway tags to railway platforms as their raison d'etre is to be walked on.

Hi
Could you reinstate NCN 4 relation please

way/893927558#map=18/51.41362/-0.30687

Hi
Could you reinstate NCN 4 relation please.
way/891716769#map=17/51.39425/-0.41857

Hi
Could you please reinstate NCN 4 relation.
way/893915272#map=17/51.43732/-0.61472

Did you mean to add a bridge tag?
way/893915273

Hi
All railway=stations are mapped. Please don't add duplicates. This is a building=train_station.

way/940677432#map=18/51.60919/-0.00041

Hi
please use the tag roller_coaster=track instead of railways for roller-coasters.

Hi
Could you be a bit more descriptive for your changset comments than Local knowledge please. It helps other mappers

Hi
Is this a miniature railway? Dodgems?

Hi
Could you take a look at your edit in this area? You appear to have a railway track crossing a platform & squashed a few buildings together.

All public transport station are mapped please don't add duplicates.

Hi
This edit appears to have broken NCN24. Could you take a look at it please.
relation/192467#map=16/50.9651/-1.3710