PROC MIANALYZE generates incorrect t-test and F-test p-values when the degrees of freedom are very large.
Note that, when the computed degrees of freedom are larger than the complete data degrees of freedom, it is recommended that you specify the EDF= option in the PROC MIANALYZE statement to use adjusted degrees of freedom. For additional information, see the Combining Inferences from Imputed Data Sets section in the SAS/STAT User's Guide.
You can reduce the risk of obtaining incorrect p-values by using the EDF= option. However, there is no certified workaround for this issue.