OK, this just got more confusing.
The nicely formatted table shows up if the data frame is grouped, but not if it does not.
For example, the following code does lead to a standard, non-pretty output:
tibble(x = c("a", "b", "c"), y = 1:3)
while the next code does lead to a pretty output like I saw two days ago under the old R
tibble(x = c("a", "b", "c"), y = 1:3) %>% group_by(x)
However, the following one does not lead to a pretty output
tibble(x = c("a", "b", "c"), y = 1:3) %>% group_by(x) %>% ungroup()
Has anyone else encountered this issue?