Help w/Tricky Issue: Disconnected Table DAX Bucketing

Hi there,

I've tried everything, & I'm at the end of my wits with this SSAS Tabular Model project. I think I'm getting accurate results now, but it's extremely slow and I can't pin down why. Any help would be immensely appreciated!

Here's a link to a Power BI .pbix file with sample data:
drive.google.com/file/d/128rvGqMmCFjvAUBMmr9x06Z1fjStihJW/view?usp=sharing

High-level, we need to get a Document's "Outstanding Balance", convert it to USD, then filter into an Aging Bucket. Here are the detailed steps:

Calculate the Outstanding Balance for a Document in the functional currency

• The main table (Collections) has a unique structure. It includes the original Document (e.g. Invoice) and the Applied Document (e.g. Payment) on both sides of the table, that way you can find the Outstanding Balance for either by just summing the amount per Document.

 Find the appropriate exchange rate & convert the amount to USD

• Exchange Rates are updated monthly, and amounts need to dynamically reflect the latest rate

Place the resulting amount into an "Aging Bucket" (e.g. 15-30 Days, 90+ Days, etc)

• Calculate Days Overdue based on the Document[Due Date], then filter into a disconnected 'Aging Bucket' table
• I have a hunch this is where the efficiency issue is coming from

 Dynamically alter all of the above based on an "As Of Date" table filtered by the user

• Users need to see the data based on a historical date, so all of the above needs to adjust based on that selected date

Measure:

Outstanding Balance (USD) = 

VAR AsOfDate =  MIN( MAX('xAs Of Date'[As Of Date]), TODAY() ) // Earlier of [the latest As Of Date in the original filter context] or [Today]. Use MAX so it still works when rolled up to year or when there is no filter applied

VAR AsOfMonth = CALCULATE( 
                        MAX( 'xAs Of Date'[Month Start Int - As Of] )
                        , 'xAs Of Date'[As Of Date] = AsOfDate
                )

VAR AsOfDates = CALCULATETABLE(
                        VALUES('xAs Of Date'[As Of Date])
                        // The Collections table structure requires that we SUM all prior transactions to get the Outstanding Balance for a Document
                        // So we must override the As Of Date filter to include all dates before the most recent As Of Date, defined in the MaxDate variable above
                        // Otherwise, we would only get transaction amounts within that specific date range
                        , 'xAs Of Date'[As Of Date] <= AsOfDate
                )

VAR Aged =      FILTER( // Filter to dates within the Aging Bucket, based on the Due Date in relation to the As Of Date
                        VALUES('xDate - Document Due'[Document Due Date]),
                        VAR DaysOD =    DATEDIFF( 'xDate - Document Due'[Document Due Date], AsOfDate, DAY )
                        RETURN          COUNTROWS( // Second FILTER argument must be a Boolean value
                                                FILTER( 'Aging Buckets'
                                                        , SELECTEDVALUE('Aging Buckets'[Lower Bound]) <= DaysOD && DaysOD <= SELECTEDVALUE('Aging Buckets'[Upper Bound])
                                                )
                                        ) > 0
                )

VAR Docs =      CALCULATETABLE(
                        VALUES(Document[Document Key])
                        , KEEPFILTERS(Aged)
                        // Exclude unnecessary Documents based on the As Of Date filter context
                        , KEEPFILTERS('xDate - Document Date'[Document Date] <= AsOfDate) // Didnt exist yet
                        , KEEPFILTERS('xDate - Document Settled'[Document Settled Date] > AsOfDate || ISBLANK('xDate - Document Settled'[Document Settled Date]) ) // Already settled
                )

VAR Balance =   CALCULATE( // If the currency is already USD, we can avoid the rate calculation below & just use the Functional Amount measure
                        VAR USD =   CALCULATE(
                                            SUM(Collections[Functional Amt])
                                            , KEEPFILTERS(Entity[Entity Currency] = "USD")
                                    )
                        VAR Intl =  CALCULATE(
                                            SUMX(   Entity,
                                                    VAR FxRate =    CALCULATE( // Use Context Transition to find each Entity USD Rate during the iteration
                                                                            VALUES('USD Consolidation Rate'[USD Consolidation Rate])
                                                                            , 'USD Consolidation Rate'[Month Start Int] = AsOfMonth
                                                                            , USERELATIONSHIP( Entity[Entity Key], 'USD Consolidation Rate'[Entity Key] ) // Temporarily activate the inactive relationship
                                                                    )
                                                    RETURN          FxRate  *   CALCULATE( SUM(Collections[Functional Amt]) )
                                            )
                                            , KEEPFILTERS(Entity[Entity Currency] <> "USD")
                                    )
                        VAR Final = USD + Intl
                        RETURN      Final

                        , AsOfDates
                        , KEEPFILTERS(Docs)
                )

VAR Final = IF(ROUNDDOWN(ABS(Balance), 0) = 0, BLANK(), Balance) // Hide 0 Balances & pennies remaining from bad GP data

RETURN      Final

Relationships:

I'm completely stuck so thank you so much in advance for any help!