Update-1: The problem does not seem to exist in Intellij 2019.1.4 but does in 2019.2.4.
There is some incompatibility/issue when using fish as the terminal shell command in jetbrains ide's. in some cases. See link at the bottom for a quick visualization of the problem.
It doesn't happen for every command and isn't related to a particular command (have made up bogus command lines and still see the problem) the updating of the line feels like the days of using modems and being able to watch the cursor move across the line. It appears to be doing this to do ?syntax? highlighting of the text. I can get the problem either when doing an up arrow or with a cut and paste of the same command. Occasionally, I seem to get stuck in the mode (sort of feels like an insert mode) and every command then starts to fill slow and you can see entire line getting updated for each character typed.
Turning on debugging in fish doesn't reveal anything (to me) as the debugging isn't firing out information as the update is occuring.
Other observations. 1) No problems in iterm. 2) Happens in Pycharm and Intellij both. 3) Trying older versions of Intellij
I normally can figure these things out with a bit of brute force, stepping through the code, google searches etc, but not making any progress to even figure where to start looking. I expect it is largely an issue with intellij ide's and the way it communicates with shell's in the terminal. I didn't change anything recently (that I remember) and have always had shell integration (in intellij terminal configuration) turned off.
I uploaded some animated gifs which do a better job of describing/showing the problem in action.
I also have a lot of ide and fish plugins and have been slowly turning them off to see if I can improve the situation and plan to maybe step back a few releases of intellij to see if that helps.
Thanks in advance for any pointers / help.