After digging around a bit more I realized that the problem (for me) was that my repo was pointing to Bioconductor v3.7, while the treeio I'm using came from v3.8. Once I reset my repository
setRepositories(addURLs = c(BioC = "https://bioconductor.org/packages/3.8/bioc"))
everything worked fine. I am not familiar with mzr, so I have no idea whether the same approach would work there, but it might be worth a shot.
Kent