Critical warnings are generated as a result of Vivado pulling in overlapping constraints from example_top.xdc and <user_design>.xdc. The example_top.xdc constraints should only be used with the MIG generated example design and the <user_design>.xdc should only be used without it. This also occurs when using the "Open IP Example Design" option in the Vivado GUI.
To work around the critical warnings, you can run the vivado.tcl script provided in the /example_top/par/ or /user_design/par/ directories. The overlapping constraints can also be removed from the XDC file to bypass the critical warning messages or ignored.