I report here 3 issues with the generic gradient editor that may be related.

ISSUE 1
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SUMMARY
Krita sometimes fails to add a new gradient to the resources via the "+" button in the generic gradient editor.
It seems to happen only with segment gradients, stop gradients seem to be copied ok.

STEPS TO REPRODUCE
1. Open Krita, create an image and add a gradient fill layer
2. In the fill layer dialog activate the "Gradient Colors" tab
3. Choose a segment gradient, modify it if you want and then click the "add gradient" button

OBSERVED RESULT
A new copy of the gradient is not added to the presets.

EXPECTED RESULT
A new copy of the gradient is added to the presets.

ISSUE 2
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SUMMARY
Updating a segment gradient in the generic gradient editor seems to work ok, but the thumbnail is not updated/regenerated. Sometimes it seems to update but with the thumbnail for the previous version (hard to reproduce consistently). If the gradient is a stop gradient the thumbnail is updated.

STEPS TO REPRODUCE
1. Open Krita, create an image and add a gradient fill layer
2. In the fill layer dialog activate the "Gradient Colors" tab
3. Choose a segment gradient, modify it and click the "update gradient" button
3. Repeat more times step 3 with the same gradient. Sometimes the thumbnail is updated with the previous version

OBSERVED RESULT
The gradient seems to be updated but the thumbnail doesn't.

EXPECTED RESULT
Both the gradient and the thumbnail are updated.

ISSUE 3
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SUMMARY
Another issue is a crash that happens when we update a gradient first and then we try to add a new one based on that updated gradient. This happens with both gradient types. The output is: 
ASSERT: "resource->version() <= 0" in file [...]/libs/resources/KisResourceLocator.cpp, line 346

STEPS TO REPRODUCE
1. Open Krita, create an image and add a gradient fill layer
2. In the fill layer dialog activate the "Gradient Colors" tab
3. Choose a gradient, modify it and click the "update gradient" button
4. Click the "add gradient" button

OBSERVED RESULT
Krita crashes.

EXPECTED RESULT
A new copy of the gradient is added to the presets.

SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux
KDE Plasma Version: 5.21.5
KDE Frameworks Version: 5.82.0
Qt Version: 5.15.2