In a previous cross-sectional study using the tablet-based Oxford Cognitive Screen-Plus (OCS-Plus), deficits in delayed memory, attention, and executive functioning were identified in working-age patients with post-COVID-19 syndrome (PCS) following infection in 2020 or early 2021. Initial assessment occurred approximately five months after infection. To examine short-term longitudinal trajectories, patients were reassessed several months later. Eighty-one patients with PCS (mean age 46.6 years, 64% female) completed OCS-Plus assessments at baseline and after a median follow-up of 4.4 months. Cognitive change was analysed using Wilcoxon signed-rank tests and equivalence testing (± 1 SD of reference scores) to assess clinical relevance. Associations between cognitive change and changes in depression and fatigue were examined using bootstrap-corrected multiple regression. No significant change in cognitive performance was observed between baseline and follow-up across any cognitive domain (all p > 0.3). Equivalence testing indicated that observed differences fell within predefined bounds of clinical insignificance (all p < 0.01). Changes in depressive symptoms and fatigue were not associated with changes in cognitive performance. Across the observed follow-up period, domain-level cognitive performance remained stable, with no evidence of short-term spontaneous improvement. These findings suggest short-term longitudinal stability of cognitive impairments in PCS within the limits of screening-based assessment and the follow-up interval studied, supporting the value of continued cognitive monitoring in affected individuals.