Hi Slabbi,
Thank you very much for your help. Below I'll explain the solution so others can fix a similar issue.
Actually, in my case the uddeIM Notifier module is only installed *once* according to the "Extension Manager: Manage" list.
However, in "Module Manager: Modules" I by accident had assigned the uddeIM Notifier to two different module positions for the *same* menu items (in this case the Kunena menu), and *that* mistake triggered the error. So, the fix is to *avoid* duplicate menu assignment in the Module Manager.
Although it might not seem a bright idea to assign a module like the uddeIM Notifier to two different positions on the same page, this might actually come in handy for certain page layouts. Hence, I suggest that you consider to implement a sanity check that identify whether or not it's required to redeclare PHP functions
Anyway, things work perfectly as expected now.
Thanks again !!!
/Jacob