If you're using virtual environments (venv), are you sure you installed argon2_cffi into the same virtual environment? What happens if you run Octoprint server via the CLI (octoprint serve -v) instead of the daemon?
I am DIW also since 1.8.3 or 4
no password or name is valid. 3 instances on 2 rock64's are now DIW, Cant''t login to the web page at localhost:5000, or from another machine at rock64:5000 both of which worked with 1.8.2.
And as an additional seemingly unrelated, clue cura 5.2.0 beta for linux is crashing at the file save after a simple .stl is sliced. AND restoring to 5.1.0 which has been working well, but now 5.1.0 is also locking
up, responding only to a ctl+c from the terminal that started it. The save to disk bar changes color
slightly when clicked on after the slice, and its DIW until the terminal that started it gets a ctl+c.
So my theory is that some other library it uses, has been updated, and broke both cura and octoprint in the last 3-5 days.
cura is normally ran on this machine, and the gcode is then saved over my local network directly to the "watched" directory on which ever printer I'm feeding.
maybe you forgot to update haproxy settings too, as you only pasted pip on your reply. Or maybe you should try to downgrade to 1.8.3 and apply fix before going to 1.8.4. Or paste the error message on pip install. But that pip force reinstall has worked for others (make sure that you have activated venv before runnin pip). Or paste the error message when you use command line to set the password (octoprint user password admin).