Managing HR software deployment across multiple Dell workstations in Pakistan

Been dealing with a bit of a headache lately. We rolled out a new HR and payroll software setup across our office which runs entirely on Dell Optiplex machines and the experience has been inconsistent across workstations.

Same software, same build, different behavior on different units. Some machines run the payroll processing without any lag, others hang noticeably during batch processing cycles. We are using Vertex HCM for attendance and payroll and the vendor says the issue is hardware side, our IT says it is software side.

Has anyone dealt with performance inconsistencies running business software across a mixed batch of Dell desktops? Wondering if this is a BIOS setting, RAM configuration, or something else worth looking at before we go back to the vendor.