Error (18855): Atom location conflict. Nodes "input/output port name" and "input/output port name" from partitions "Partition A" and "Partition B" are placed in the same location, IOOBUF_{XY location}

In the Quartus® Prime Pro Edition Software, you may see an error like this one when a bidirectional port drives logic in a child location from the root partition. This means the IO buffer is placed in the child partition. When this partition is used in the core partition reuse flow, the IO buffer location can conflict with IO buffer locations in its parent partition.

To avoid this error, perform either of the following actions

• Ensure that there are no bidirectional ports at the interface of an exported partition, that way no IO buffers will be inserted there. This may involve decomposing the bidirectional logic in the top partition and running separate input and output signals where they are needed.     
• Ensure the IO buffer placement is consistent across developer compilations. This means setting location, placement or routing constraints on any partition that contains IO buffers and ensuring their locations don't conflict with those in their parent partitions.