Formula Checkbox not checking all the time based on formula

These are the fields that I have:

Checkbox Formula Field: Mod Finalized Required

Case(false,

ToText([Event Modification(s)])="", true)

Checkbox Formula Field: Materials Finalized Checkbox

If([materials_finalized]<Now(), true, false)

Date Formula Field: Session Date

ToDate([session_start_time])

Date Formula Field: Materials Finalized Date

ToDate([materials_finalized])

Those all work fine. What doesn't work is the following formula Checkbox field:

Materials Finalized on Time

If([Mod Finalized Required]=true and [Modifications Finalized Checkbox]=false, false,

    (WeekdaySub([Session Date], [Materials Finalized Date])>=2), true)

This field should have the following outcomes:

If the Mod Finalized Required is checked and the Materials Finalized Checkbox is not checked: not checked

If the Mod Finalized Required is not checked and the Materials Finalized Checkbox field is checked: checked and

If the Materials Finalized Date is equal to 2 or more business days before the Session Date, then check the Materials Finalized on Time checkbox.

It works for the most part but not on all. Can't figure out what is wrong.