Sluggish Milestones blocked by bug?

[mileswest07]

On my save file, I was able to achieve the 20-boost Sluggish Milestone, eventually. However, attempting to work towards the 15-boost Sluggish Milestone, I run into a problem with the Boosters.

My strategy is to get 15 Factor Boosts and then prevent Bulk Boosting (Bulk Boosting option set to OFF) and using Challenge completions to increase factors (with Factor Boost If Possible Upon Entering a Challenge set to OFF). So that should prevent any unintended Factor Boosts, right?

It seems that this prevents players from attempting to farm Incrementy since the Factor Boost reached (but not Gained) will apply no matter what happens. This bumps the Factor Boosts up to 16, locking me out of attempting the Sluggish Milestone unless I collapse.

Bug? Or missed option somewhere / user error?

Save file attached for testing:
Ordinal Markup Save.txt