Thank you for the samples!
I could not reproduce those warnings on our side based only on the samples you sent.
I used oXygen XML Editor v20 with the built-in DITA-OT 2.x and the predefined (unmodified) DITA Map WebHelp Responsive scenario.
However, after further investigation, it seems that the messages of this type are reported by an XSLT processor when encounters two or templates with same import precedence and priority. See the M. Kay answer from the next thread:
https://stackoverflow.com/questions/236 ... nt-in-xslt
Most probably you have a custom DITA-OT, or an XSLT customization that generates this.
So you have to identify these templates and set a priority for them if they are located in your customization.