vib

The issue "Layer Effects, 3D Effect: setting Fill Opacity to 0% doesn't turn the fill transparent" (REF: AF-1668) has been fixed by the developers in internal build &quot2.4.0.2222&quot.
This fix should soon be available as a customer beta and is planned for inclusion in the next customer release.
Customer beta builds are announced here and you can participate by following these instructions.
If you still experience this problem once you are using that build version (or later) please reply to this thread including @Serif Info Bot to notify us.

Hi @Old Bruce,
It becomes transparent because the Fill Opacity was still set to 0% before you removed the effect. So before removing the 3D make sure to set the Fill Opacity to 100% again then remove it and you should see the ellipse.

@vib
Welcome to Affinity Forums
I've reproduced the issue here and have logged it to be checked by the dev team. Thanks for reporting it.

Imo, this is a rather big and silly oversight. When using AP as a painting tool, this can be a very much used feature. I use it about a hundred times per painting. 
Anyway, I have an easier workaround than the flood fill tool, because let's face it, who has the time to switch tools in mid painting flow? 
It's simple: Select all layer content (ctrl+a). Now pressing delete or backspace will result in the layer being cleared, but not removed. 
While painting in AP I make it a habit to always paint with the entire layer selected, so I can just press delete at any time. This prevents me from wanting to commit suicide when doing stuff like trying out brushes.
But seriously, this workaround should not be required at all.
Good luck!

Layers panel > Hamburger menu (top right) > Show Group Thumbnails.

I've been searching for some time for a way to give Export Slices in Export Persona Mode a keyboard shortcut, so I can easily export all art works with 1 keypress.
So far I found no possibility to set this shortcut.
It simply doesn't exist in File > Preferences > Keyboard Shortcuts
It should be assignable since it's one of the most useful commands in Affinity Designer :)
 

@JQL
In some cases in may help to use artboards for this. You can arrange the different states of your images on different artboards, and give the artboards matching names. Elements that are repeated and used on every artbord can be arranged as symbols in Designer, so that changes on one artboard changes them on all other ones.
At least for a project with gamecards this worked quite well for me. It's not the same as using layer compositions and exporting them as files. On the other hand, you can see all you variations at a glance, without switching through all composition states.

It would be very useful if the export persona allowed us to choose what layers were exported for each slice.
I do complicated graphs that build up from simpler ideas. So it is useful to put the basic graph on one layer, some enhancements on another layer, and perhaps point out some specific features on a third layer. I then want to export this as three separate images: Just layer 1, Layers 1+2, and Layers 1+3. At the moment the only way I've found to do this is to manually change the visibility of the layers and the name of the exported file and then export one file. This process needs to be repeated three times in my example.
I can also imagine that icon designers would find this useful. They could have a layer with the basic icon and then other layers with overlays (check marks, or plusses etc). If there was the possibility of selecting which layers were visible for each slice they could set up batch exports for these.

@ahnaySymbols are the only practical way to do non-destructive vector symmetry in Designer that updates live as you go along. Though, the ultimate method is only achievable by owning all three programs while working in Publisher. There you have easy access to Linked Layers, a Photo feature which is basically Symbols but with more custom options, and they work with Compound Layers for non-destructive booleans, unlike Symbols. Here's a brief tutorial I made showing the power of Linked Layers:
 
If you ask me, this feature should frankly be a Designer feature as well. It is insanely powerful and is a lot better than the Illustrator method, especially since it can be combined with Symbols, Groups, Compound Layers, etc. to create very complex patterns and be completely non-destructive.

Thanks @Dan C for the report and the workaround. I've been using mask layers as a workaround instead. That provides the same end effect while letting me keep the anti-aliasing. But it's nice to have more options, thanks!

On the Layer Effects window, set the "Fill Opacity" at the bottom to 0%.

Myself I think the search was put in but not connected to search in anything other than some of the words in the panels. Then it was forgotten. It is utterly useless.

Hi @vib,
Welcome to the Affinity Forums
I can confirm that the Search in the top right of the Preferences dialog is not designed to search for specific keyboard shortcuts, it is designed to find the category names shown in the Preferences dialog, and any sub labels from within these categories.
However it is logged as an improvement with our developers to expand this search functionality to include the keyboard shortcuts section, so I will be sure to add a 'vote' for this in our internal development log for you now.
I hope this helps!