List limit 5000. Filtered value on lookup column number not working

Greetings!

We have a list with more than 5000 lines of records (5064 to be precise). Due to sharepoint system constraint (what I understand and based on the message displayed), we are trying to filter this view on a lookup column (that is pointing to a different list value). This lookup value is numeric (Number format).

With this filtered view, the list should be reduced by atleast 1000 lines, and hence should be below the threshold constraint of 5000 lines.

Unfortunately, after filtering, we continue to get the error:

This view cannot be displayed because it exceeds the list view threshold (5000 items) enforced by the administrator.

We developed another view with just filtered list of around 1000 lines, but filtered on a different column within the same list. That worked fine.

Any advise?