remote: Verifying deploy... done.
fatal: protocol error: bad line length character: fata
error: error in sideband demultiplexer
This just randomly started showing up. My changes are being saved in git and pushing successfully to Heroku. I have no idea what this means or what caused it as I have not done anything new at all.
Just had this issue myself. What worked for me was this response directly from Heroku Support
$ Upgrade GIT on your local machine
$ heroku plugins:install heroku-repo
$ heroku repo:reset -a <app-name>
$ git commit --allow-empty -m "Reset repo"
$ git push heroku master
Having spoken to Heroku support recently regarding this, you can pass the below environment variables when pushing to your Heroku remote to reveal more about what's going on:
GIT_CURL_VERBOSE=1 GIT_TRACE=1 git push https://heroku:key@git.heroku.com/app-name.git develop:develop
Cleaning the heroku repo and then pushing again from scratch did the trick for me.