I have a CRON job scheduled for my repo, and I haven’t pushed any recent changes in a month. Recently the build for R version 3.4 and 3.5 started failing. The remaining version are building as expected.
https://travis-ci.com/github/dachosen1/formulaic/builds/170607214
If you changed nothing, most probably, some dependencies and/or external resources changed.
In this case, it’s a problem with rmarkdown v2.2, it started using an API that’s only available since R 3.6:
rmarkdown