If there's multiple POs associated with PMProject or ARRegister it's going to duplicate lines.
In that case you need to group it and use Min or Max aggregates of fields you are pulling in.
If you are also trying to get a sum as well as a min In this scenario, sometimes you can divide by a count.
If you need to use aggregates in a formula be sure to aggregate them by themselves in an earlier line first.
These types of GIs can be quite frustrating and run slow.
Until we can create Derived tables with GIs, it's just not an easy GI.
Depending on the use case, an alternative may be to add a side panel to show related POs.