Currently, the widget templates are not updated on upgrade, as we don't have a mechanism for merging templates.
Ones you update a widget template, it is persisted in the database and used instead of the default one. Any change in the default template, coming with the newer version, does not affect the persisted customized template, which in some cases is expected behavior. We know that, in other cases, this could cause some issues with missing functionality on customized templates (excluding the case with the error reported in this thread - it is a bug), and we will try to address this in the future.
Maybe you have changed this template in the past, otherwise it should not be persisted.
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