Savings Plan Table - Up to Threshold Limit Understanding

I am trying to understand on the Savings Plan Table, how the Up to Threshold Limit works. We had a few employees who did not have their 401K after tax deductions taken.  I read around on the setup, and identified the cause being related to the Up to Threshold limit on the setup for our 401K.  It was set at 50% Total Investment (Btax and Atax was also 50%).  Once I changed the Total Investment to anything greater than 60% the after tax amount appeared on the paycheck, anything less, the deduction maximum was met for a handful of employees.

Our EE YTD Earning Threshold is set to $0.00