The vignette title specified in \VignetteIndexEntry{} is different from the title in the YAML metadata. The former is "Solving Model Instability: A Case Study in Time Series Estimation", and the latter is "Numerical stability enhancements in beta autoregressive moving average model estimation". If that is intentional, you may set options(rmarkdown.html_vignette.check_title = FALSE) to suppress this check.