When managing an existing filter, you need to make sure you either delete an existing limitation, or edit and save the parameter.  

Edit the existing filter by using Manage > Edit

The only limitation on this filter is to show inspections due in the next two months, but also includes past due inspections.  Select it, then change the parameters.

 

Click Update  - then Save your changes

***The results aren't what I expected after saving my filter***

1) was the parameter already in use? If so, delete the limitation, save filter, then add it back/update/save.

2) is this a field you've used before? Are you confident in the results? Sometimes limitations skew results.  Too many limitations can yield very limited results.