I ended up finding a solution. Leaving out the default value in the Data Model parameters, and choosing 'All' in the parameters section in the Report solved this issue. Both parameters are now correctly defaulting to the 'All' that means All Column Values. Thanks, all, for your help!

Thanks for the quick response! Unfortunately, when we remove the 'All' as a default value, it defaults to the first column value from the LOV. It does not default to 'All'. Additionally, I've confirmed there is no extra space in the string 'All'. Any other suggestions?