Switching Measures Depending on Selected Dates

Hello guys, hope you are doing well. 

I had a call log table for one system, then we moved (on 11/1) to another system hence we have another call log table. I have a requirement to merge both data so they can view the right numbers depending on the date they select.

My problem is that when I select data before 11/1/23 (even mulltiple values) the new measure that I've created works, but when I select multiple values (in this case only 11/1/23 and 11/2/23) is not aggregation the values, it only works if I select a single date.

I'll post a few pictures and below the information:


(this is the view before 11/1/23, you can see that the "Combined AHT" shows the total when I select more than one day)



This is after 11/1/23 but only selecting 1 value. The "Combined AHT" total works the same way as the "New AHT" (this one is only taking data on or after 11/1/23).



And here is when I select multiple values after 11/1/23. You can see that the aggregation is not working (it should be 472).




Lastly, here is the measure I'm using for the "Combined" view.

If you please can help me out with this, I'd appreciate it a lot.

Thanks!