Sustainable human resource management is critical in infrastructure sectors, yet firm-level resilience may conceal uneven health burdens within the workforce. This study examines a »resilience paradox« in a large Slovenian energy company using a two-level design. At the macro level (2012–2022), we explore associations between absenteeism categories and three efficiency ratios. At the micro level, we estimate a Poisson quasi-maximum-likelihood model with log planned hours as an exposure offset and cluster-robust inference on a balanced group-month panel (960 observations) built from 82,033 payroll records (2018–2022). Macro indicators remain stable, and we do not detect negative correlations between absenteeism and efficiency ratios, suggesting that operational continuity can be maintained despite absence shocks. However, micro-level estimates reveal pronounced inequalities: compared with employees aged ≤30, absenteeism rates are higher for ages 31–45 (incidence rate ratio—IRR 1.335), 46–55 (IRR 1.538), and >55 (IRR 1.829). Field/operational groups have higher rates than office/administrative groups (IRR 1.829), and female groups show higher rates than male groups (IRR 1.252). During COVID-19, absenteeism declined for office groups (IRR 0.840), while the additional effect for field groups was small and statistically uncertain (interaction IRR 1.179). The results call for targeted sustainable HRM interventions addressing aging, occupational risk, and equitable health protection across job types.