icemelting

Thanks for the info & doc provided, this is exactly what I needed!
I believe this is a bug, there is no reason I can see for the masks position within the group to affect the partial transparency being applied, so I'm logging this directly with our developers now.
I hope this helps

Here some features posted:
 

No problem at all, more than happy to help!
When masks are grouped with Affinity, they will only apply to other layers within the group, allowing the flexibility of editing options, such as shown in my example.
The mask becomes 'tied' to the Group, rather than affecting the whole document.
I'm not seeing this here, but this could be cased by either a) a blend mode applied to the mask, or b) partial transparency in the mask. Could you please provide a copy of your document where you see different results based on the masks position?
Placing a layer at the top of the stack will ensure it is applied to all layers beneath. When nesting an adjustment, it will then only affect the layer it is nested to, or multiple layers contained within a group, if nested to a group layer.
I hope this clears things up

Hey @Wosven,
I’m totally on your side with this one. This feature of expanding the mask with the crop already works good with the iPad version of Affinity Photo.
I’m new to this forum. Is there a way in which we can request for features of suggest changes? If you are comfortable with the procedure, kindly take this forward as a feature request/suggestion. If it’s much, kindly direct me, so that I request for the same. Thank you.
Regards,
Gokul PM

About the original problem, of mask using only the visible part of an image (as in ignoring bleed in APub, or once cropped), it would be interesting if the mask was effective on the whole image in each case.
With this, we can widen a visible area, move an image in an image frame, re-crop larger, etc. with few adjustements to adapted the partially painted margins now visible.
For example, if I used a gradient on a mask, it would go behond the visible part of this image, since the mask would cover the full image. And I would be able to crop differently/move from the bleed, etc. without complexe work to recreate the missing parts we usually get.

You can simply create your adjustments and with the mask layer at the top of the layer stack, group the mask with the adjustment layers - this way the mask will only affect the adjustment layers  -
(original)

(mask on)

(mask off) -

I hope this helps  

There is a 'Reveal' setting on the context toolbar that should reveal the whole canvas, but unfortunately it doesn’t appear to be working.

I can confirm that crop tool sometimes / always doesn't reveal to area outside the crop (in contrast to the desktop version). Assuming a bug here.
As a workaround, If you want to see whats outside the cropped area, there are two options:
Document>Cancas>Unclip Canvas
This reveals the complete document is the shorted option Using the crop tool, switch to the 2nd page of the context menu, deactivate "darken". Unfortunately, this seems not to work currently. Assuming a bug here. Additional bug: When i click "Reveal", the context menu witches back to the first page. filed a bug report
 

If I select the mask and paint black over the unapplied area, the adjustment layers vanishes from that region. But are there any other ways to do this automatically when we expand the crop?
Not that i know.
But i think there is a faster way than painting. You decide.
Taking your image as an example, what i usually do is make a selection with the Rectangular Marquee tool and with the mask selected fill with the primary/secondary colour.
I assigned a shortcut for that.
Edit > Preferences > Keyboard shortcuts > Photo (Edit)
- Fill with primary colour
- Fill with secondary colour
The "D" and "X" keys can also be handy.
In your example you dont even have to use the marquee tool. I just pretended there was some masking in there.

If you change the units from pt to px for numeric input you get this effect.
This might happen by accident 

Could it have something to do with the Pressure profile setting? You have set the end point to approx. 50%.

Welcome to the Serif Affinity forums.
If you tap the number rather than using the slider you should get a pop up keypad that will let you enter the value you want.

That does not happen for me. The value I enter via the popup number pad is the value that is entered in the Stroke studio.