First time I've experienced this problem. Have un/re-installed R, Rstudio multiple times, which does not seem to work.
---
title: "Missing Tabs"
output: html_document
---
## Tabset here {.tabset}
### tab1
```{r}
summary(cars)
```
### tab 2
```{r}
summary(pressure)
```
Produces a document with no tabsets:
All packages are up to date, I've tried installing the latest dev version of rmarkdown using the remotes package, but the same problem occurs. Not sure what to do here at this point.
Session info:
> sessionInfo()
R version 4.0.2 (2020-06-22)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 18362)
Matrix products: default
locale:
[1] LC_COLLATE=English_United States.1252 LC_CTYPE=English_United States.1252
[3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C
[5] LC_TIME=English_United States.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] rmarkdown_2.3
loaded via a namespace (and not attached):
[1] rstudioapi_0.11 knitr_1.29 R6_2.4.1 rlang_0.4.7 fansi_0.4.1
[6] tools_4.0.2 pkgbuild_1.0.8 xfun_0.15 cli_2.0.2 withr_2.2.0
[11] htmltools_0.5.0 remotes_2.1.1 yaml_2.2.1 digest_0.6.25 assertthat_0.2.1
[16] rprojroot_1.3-2 crayon_1.3.4 processx_3.4.3 callr_3.4.3 ps_1.3.3
[21] curl_4.3 glue_1.4.1 evaluate_0.14 compiler_4.0.2 backports_1.1.8
[26] prettyunits_1.1.1
> devtools::session_info()
- Session info ------------------------------------------------------------------------------------
setting value
version R version 4.0.2 (2020-06-22)
os Windows 10 x64
system x86_64, mingw32
ui RStudio
language (EN)
collate English_United States.1252
ctype English_United States.1252
tz America/New_York
date 2020-07-11
- Packages ----------------------------------------------------------------------------------------
package * version date lib source
assertthat 0.2.1 2019-03-21 [1] CRAN (R 4.0.2)
backports 1.1.8 2020-06-17 [1] CRAN (R 4.0.2)
callr 3.4.3 2020-03-28 [1] CRAN (R 4.0.2)
cli 2.0.2 2020-02-28 [1] CRAN (R 4.0.2)
crayon 1.3.4 2017-09-16 [1] CRAN (R 4.0.2)
curl 4.3 2019-12-02 [1] CRAN (R 4.0.2)
desc 1.2.0 2018-05-01 [1] CRAN (R 4.0.2)
devtools 2.3.0 2020-04-10 [1] CRAN (R 4.0.2)
digest 0.6.25 2020-02-23 [1] CRAN (R 4.0.2)
dplyr 1.0.0 2020-05-29 [1] CRAN (R 4.0.2)
ellipsis 0.3.1 2020-05-15 [1] CRAN (R 4.0.2)
evaluate 0.14 2019-05-28 [1] CRAN (R 4.0.2)
fansi 0.4.1 2020-01-08 [1] CRAN (R 4.0.2)
fs 1.4.2 2020-06-30 [1] CRAN (R 4.0.2)
generics 0.0.2 2018-11-29 [1] CRAN (R 4.0.2)
glue 1.4.1 2020-05-13 [1] CRAN (R 4.0.2)
htmltools 0.5.0 2020-06-16 [1] CRAN (R 4.0.2)
knitr 1.29 2020-06-23 [1] CRAN (R 4.0.2)
lifecycle 0.2.0 2020-03-06 [1] CRAN (R 4.0.2)
magrittr 1.5 2014-11-22 [1] CRAN (R 4.0.2)
memoise 1.1.0 2017-04-21 [1] CRAN (R 4.0.2)
pillar 1.4.6 2020-07-10 [1] CRAN (R 4.0.2)
pkgbuild 1.0.8 2020-05-07 [1] CRAN (R 4.0.2)
pkgconfig 2.0.3 2019-09-22 [1] CRAN (R 4.0.2)
pkgload 1.1.0 2020-05-29 [1] CRAN (R 4.0.2)
prettyunits 1.1.1 2020-01-24 [1] CRAN (R 4.0.2)
processx 3.4.3 2020-07-05 [1] CRAN (R 4.0.2)
ps 1.3.3 2020-05-08 [1] CRAN (R 4.0.2)
purrr 0.3.4 2020-04-17 [1] CRAN (R 4.0.2)
R6 2.4.1 2019-11-12 [1] CRAN (R 4.0.2)
remotes 2.1.1 2020-02-15 [1] CRAN (R 4.0.2)
rlang 0.4.7 2020-07-09 [1] CRAN (R 4.0.2)
rmarkdown * 2.3 2020-06-18 [1] CRAN (R 4.0.2)
rprojroot 1.3-2 2018-01-03 [1] CRAN (R 4.0.2)
rstudioapi 0.11 2020-02-07 [1] CRAN (R 4.0.2)
sessioninfo 1.1.1 2018-11-05 [1] CRAN (R 4.0.2)
testthat 2.3.2 2020-03-02 [1] CRAN (R 4.0.2)
tibble 3.0.3 2020-07-10 [1] CRAN (R 4.0.2)
tidyselect 1.1.0 2020-05-11 [1] CRAN (R 4.0.2)
usethis 1.6.1 2020-04-29 [1] CRAN (R 4.0.2)
vctrs 0.3.1 2020-06-05 [1] CRAN (R 4.0.2)
withr 2.2.0 2020-04-20 [1] CRAN (R 4.0.2)
xfun 0.15 2020-06-21 [1] CRAN (R 4.0.2)
yaml 2.2.1 2020-02-01 [1] CRAN (R 4.0.0)
Also created a post over at SO: r markdown - Tabsets are not rendering in knitted rmd files - Stack Overflow