library(tidyverse)
df <- structure(list(a = list(c("a", "b"), "c"), b = list(c("1", "2",
"3"), "3"), c = c(11, 22)), class = c("tbl_df", "tbl", "data.frame"
), row.names = c(NA, -2L))

# A tibble: 2 x 3
  a         b             c
  <list>    <list>    <dbl>
1 <chr [2]> <chr [3]>    11
2 <chr [1]> <chr [1]>    22

> df %>% unnest(a, b)
Error: All nested columns must have the same number of elements.