A 42-year-old woman with type 2 diabetes mellitus is enrolled in a randomized controlled trial comparing a new SGLT2 inhibitor versus metformin for glycemic control over 12 weeks. The trial protocol specifies that participants will be stratified by baseline HbA1c (≤8% vs >8%) and randomized 1:1 to each arm using computer-generated random number tables. After randomization, 5 participants in the SGLT2 inhibitor arm develop genital mycotic infections and withdraw. The metformin arm reports no withdrawals. The principal investigator decides to replace these 5 participants with new recruits to maintain equal group sizes. What is the primary methodological flaw introduced by this post-randomization replacement strategy?