In Magento, every data provider interface is rewritten by a model class.

If you Check di.xml of Magento_SalesRule of then you will find that Magento\SalesRule\Api\Data\RuleInterface is overridde by Magento\SalesRule\Model\Data\Rule.

So, is this class, might be Magento\SalesRule\Model\Data\Rule override by other class of any 3rd party module where might be ActionsHintLabel define. But this wrong way to rewrite a data model class.

Or may there are some Extension attribute concept build on Magento\SalesRule\Api\Data\RuleInterface and use for additional some work.

So, you have to check extension_attributes.xml of your e3rd party module extension_attributes.xml and find the solution by removing this extension attribute.

In Magento, every data provider interface is rewritten by a model class.

If you Check di.xml of Magento_SalesRule of then you will find that Magento\SalesRule\Api\Data\RuleInterface is overridde by Magento\SalesRule\Model\Data\Rule.

So, is this class, might be Magento\SalesRule\Model\Data\Rule override by other class of any 3rd party module where might be ActionsHintLabel define. But this wrong way to rewrite a data model class.

Or may there are some Extension attribute concept build on Magento\SalesRule\Api\Data\RuleInterface and use for some additional work.

So, you have to check extension_attributes.xml of your 3rd party module's extension_attributes.xml and find the solution by removing this extension attribute.