Hello Jean-Sebastien

Solution would be Automation action on product.template.attribute.line model, to reset value of attribute value on selection of attribute. 

1) Activate Developer mode from setting --> Click on Activate Developer Mode.

2) Go to Settings --> Technical --> Autotmation Rules

3) Create new automation rules as following

Model -> Product Template Attribute Line

Trigger -> On UI Change

When updating --> Attribute

Add An action --> python code

record['value_ids'] = False

Thanks & Regards,

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