Artcraft

I dug around, this issue seems to be present since 2017 and/or earlier, so there wont be a fix anytime soon. It's really bad since it's one important key feature when working with vector graphics and makes this program actually unusable.  It's fine if you end up with raster graphics anyway but I need vector graphics. I will have to stick with illustrator until this is solved... I hope they will solve it, has been over 5 years now.

Simpler to not do the breaking and joining - just reverse the path of the lower shape only (or both shapes simultaneously if you wish) and then Boolean Add will work.
The other Boolean operations will continue to not work or produce wrong results after the simple or convoluted procedures.
(Affinity 1.10.6 has no problem with these shapes.)

Neither do I.
However, if I use the Node tool and select each shape and then Break the Curve, Join the Curve and Reverse the Curve. For each curve separately. Then I can add them.

This is certainly not a solution. I will not downgrade my OS for one single buggy software. It's an issue with Affinity. I hope they address this soon but it wont happen, there are still major bugs out there since 2016.

I totally agree with you, eveything works fine, except Affinity products...
I ditched adobe months ago, but now, I realize that affinity is full of bugs... And I don't see any solution provided for most of them, except "uncheck hardware accelation", no software update, just tricks user side.
I'm at the point where I really consider to return to adobe.
I mean, I really don't want, but honestly I can't work in decent conditions with Affinity.

I know.
But do you understand that I don't want to spend my time on forums in order to be able to work ?  
I'm sick to do this kind of things, uninstall windows updates when all other programs works without issue, do some obscur tricks like limit affinity photo cpu usage to 6 threads...  Do I need to adapt my OS to affinity products ?
Why do the users need to do that ? Is it my job ?

Sorry for the late reply...windows 10, only happens when pressing comma , on my keyboard, NumPad has period only, not decimal (European decimal). Everything with period works, everything with comma doesn't. 

The issue is probably caused by using curves, vector brush with pressure profiles. These layers get expanded when exported, and the expanded curve is not exact, deviates in width from the original.
I put both (original and SVG) of the affected part into one document, and recolored the original to a pink color.
PS:
when you manually expand stroke, you get another deviating version (too narrow, but slightly different curve) from the result via svg export.
So probably expand stroke has an issue when curves with pressure profiles are expanded.
maybe related:

 

biber 4 bug.afdesign

Also struggling with this a lot.... Also while exporting into SVG. I don't know if I can longer use Affinity for my professional work because of it  

I dug around, this issue seems to be present since 2017 and/or earlier, so there wont be a fix anytime soon. It's really bad since it's one important key feature when working with vector graphics and makes this program actually unusable.  It's fine if you end up with raster graphics anyway but I need vector graphics. I will have to stick with illustrator until this is solved... I hope they will solve it, has been over 5 years now.

I exported my image as a PDF and it completely screwed my strokes up, because Affinity is a buggy mess. I decided to expand my strokes and to try it again. My strokes have pressure on it (I used the Vector Brush Tool) and now I have to deal with another bug, which thins my strokes and does a few other things...Does anyone knows a work around this? Rasterizing is out of option, it has to be a vector image. I found a tip here about changing size variance in brush editor but that doesn't work either.

@JET_Affinity
Plotting points is tedious and more in line with an engineering mindset. Some tasks are suited to careful, surgical point plotting, but for digital illustration which assumes an artists mindset, there should be direct intuitive drawing and painting tools. Natural, direct, efficient, intuitive.
As for your complaint about excessive points, that's a software engineer's problem, not an argument against a painting tool that creates freeform vector shapes. Consider the problem Serif had with excessive points for expanded strokes.

In illustrator owe have the scale tool to push two anchor points or nodes towards or away from each other, symmetrical and in equal amount, in Inkscape it's possible too. In Affinity Designer it seems to be an eyballing thing and I'm not an eyballing person. Is there a simple way around this? I tried with shift and alt and ctrl and don't know what else but none of these works. I'm aware of the point transform but unless it has some hidden functions I'm not aware off, it can not do the job.
Edit: found it finally, it is not point transform, for whatever reason I thought it is. it's the transform option (and hold CTRL). image n°3
 


 

It makes absolutely no sense that the origin point does not work with all transformations, rotations and flipping. It's extremely puzzling how this has been left this way for so long. It's basic things like this that really set AF back.

Yup, it prevents me from leaving InDesign and moving to all Affinity products.

Priorities are at play. And you are paying. With years of life and lost opportunities. Will you wait another year for a fix? Two? More?
They are not trying to figure out and implement cold fusion. Rather implement a working and acceptable divide operation that should have worked properly since 2015. You are waiting because they let you wait. But you will get Publisher on iPad I guess. 

no its not accurate at all, DIN A4, 300 dpi, big image, strong deformation.
Edit: Added file to attachment


FILE:
stroke.afdesign

Thanks, looks good right now... except of a few thousands unnessary nodes on my shape. Well it seems I have to wait til boolean operators get better.

(Attached file)  right click on your desktop icon, properties and at the end of the line   --legacy-wintab
 
 

(Attached file)  right click on your desktop icon, properties and at the end of the line   --legacy-wintab
 
 

(Attached file)  right click on your desktop icon, properties and at the end of the line   --legacy-wintab
 
 

Here's my v2 progress so far (haven't had much time on the computer over the last few days)
Kids v2.afdesign