Mapper failures typically have two modes. Either the failure happens during a pre-check phase or it might happen during the actual mapping phase.
Pre-check failures have explicit error messages which point to exact reason for failure, as shown in the following example.
ERROR: [aiecompiler 47-772] Inst g.kernel_a is in conflicting pblocks:(0,0) (5,5) and (20,0) (25,5).
You can trace such errors to the design element or the constraints.
Mapping phase failures typically have an error message that looks like the following.
ERROR: [aiecompiler 47-51] AIE Mapper failed to find a legal solution. Please try to relax constraints and/or try alternate strategies like disableFloorplanning.
In this case, use the following steps to either narrow down the cause of the failure if it is design-related or help the tool to find a solution if the failure is tool-related.