I think I have the same problem although as far as I can see only concerns displaying
data.frames. I think the problem (at least in my case) has to do with LOCALE settings or encodings in some way. (I have a lot to learn about such matters so bear with me if I express myself poorly...)
What I have found is that the problem only appears when my Rstudio-project (which holds my code) resides in a folder named with any special character (like the Swedish å, ä, ö). If I move the whole project folder to a folder without special characters it works fine.
I have tested it with a simple example that should display a table of a
data.frame inline in the Rmarkdown/Rnotebook document. Sure enough. it does when in a non-special-character-named folder but not in a folder named with any of the Swedish å, ä or ö.
Here's what my notebook editor would look like if the project resides in a special character folder (and running the code):
title: "R Notebook"
a <- c(1, 4, 3)
 1 4 3
a object is shown inline but not the
Unfortunately I don't know how to show inline outputs such as tables (data.frames) using formatted code in my post so I'll have to show the situation when in a non-special-character folder as a picture, sorry:
As you can see now the data.frame is properly shown as a table inline. The only difference between the two situations is that the RStudio project resides in a special character folder (with an å in its name) or not.
By the way, the html-notebook-document generated have the same problems, it is not just in the editor.
I realise I could circumvent the problem by just not using special characters when naming folders but it is nevertheless a bit anoying and anyway might provide a solution to the OP's problem.
Any input on how to handle/set LOCALE/encodings properly to fix this is highly welcome.
Oh, and by the way I'm on a windows 10 machine:
R version 3.6.1 (2019-07-05)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 17763)
Matrix products: default
 LC_COLLATE=Swedish_Sweden.1252 LC_CTYPE=Swedish_Sweden.1252
 LC_MONETARY=Swedish_Sweden.1252 LC_NUMERIC=C
attached base packages:
 stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
 compiler_3.6.1 magrittr_1.5 htmltools_0.3.6 tools_3.6.1
 base64enc_0.1-3 yaml_2.2.0 Rcpp_1.0.1 stringi_1.4.3
 rmarkdown_1.13 knitr_1.23 jsonlite_1.6 stringr_1.4.0
 digest_0.6.19 xfun_0.7 packrat_0.5.0 evaluate_0.14