I upgraded my Ubuntu recently from 19.04 (Disco) to 19.10 (Eoan Ermine). At some point, I noticed that Shift+Tab stopped working in vim. I use nvim and have Tab configured to move to the next tab and Shift+Tab configured to move to the previous tab. Tab worked, Shift+Tab didn’t.

It’s two lines in my .vimrc:

nmap <Tab> :tabnext<enter>
nmap <S-Tab> :tabprev<enter>

Maybe it’s nvim?

At first, I suspected it’s a problem with nvim since I upgraded it as well and there is some old article mentioning how to get Shift+Tab to work. While old it provided some nice way of checking if vim has received the keys. If in insert mode you press Ctrl+V it tries to write the literal character of what you pressed into the file instead of interpreting it in some way. Again, for Tab it worked, and for Shift+Tab it didn’t.