I'm going to be a little vague in this report because I do not have 100% of the technical details. This may be an RFE/CR and not a bug but I can assure you Shaper Origin users who use AD need this functionality. I will follow template and see what becomes of it.
Are you using the latest release version?
(here's how to check) yes
Can you reproduce it?
(if you cannot then we may struggle to also, making it even harder to fix) yes
Does it happen for a new document? If not can you upload a document that shows the problem? yes
If you cannot provide a sample document then please give an accurate description of the problem for example it should include most of the following:
What is your operating system and version (Windows 10, OSX Mojave, iOS 12 etc)? Big Sur
Is hardware acceleration (in Preferences > Performance) ON or OFF ? (and have you tried the other setting?) n/a
What happened for you (and what you expected to happen) Export SVG and expect the icon to show a thumbnail of the image
Provide a recipe for creating the problem (step-by-step what you did). see below
Screenshots (very handy) or a screen capture/video. See below for detailed steps
Any unusual hardware (like tablets or external monitors or drives that may affect things) or relevant other applications like font managers or display managers. no
Did this same thing used to work and if so have you changed anything recently? (software or hardware) never worked
STEPS TO REPRODUCE:
1) Draw object
2) Select "File | Export | SVG" with following settings:
3) Note that in the OS, the thumbnail looks correct
4) However, if you upload to ShaperHub (place to send SVG files to the Shaper Origin) and upload, you will notice there is no thumbnail.
Now I know this sounds like it is out of Affinity's hands and Shaper needs to fix. The reality is AD is the only SVG tool I've seen that doesn't do this correctly. Additionally, users have written a Python script (and a web tool) and apparently it is as simple as adding a 'viewBox' parameter to the SVG.
https://community.shapertools.com/t/affinity-designer-script-to-add-thumbnails/6384
Could we please get this added to Affinity Designer so all of us Shaper Origin users can stop using external tools and scripts that interrupt our workflow? The aforementioned Python script is available on the link I pasted as well as notes from the author.
Thanks for your consideration.