Ubuntu 18.04 input slow when Portuguese (Brazil) layout among keyboard input sources

The comment below was the solution that worked for me. I found it at https://bugs.launchpad.net/ubuntu/+source/meta-gnome3/+bug/1777708 and the author of this answer is Pedro Palhares.

After being annoyed by this bug for a long time, i started digging and found a workaround. Today i found that the bug is only present when i'm using certain keyboard layouts ("Portugues (Brasil)") and was not present when i changed the layout to EUA and language to English (need to set them both to English).

After some digging i found out the culprit is the ScrollLock key and that can be fixed by editing the layout file, which in my case is found at /usr/share/X11/xkb/symbols/br. The only modification i did was to remove or comment the line: modifier_map Mod3 { Scroll_Lock }; After that, set the language and layout back to Portugues (Brasil) and the problem was gone!

No more delays between typings. (Fedora and Ubuntu)

The input for passwords and text is now working well, without delays. Maybe some Ubuntu/gnome update (dont' know which exact update fixed it - was using cinnamon and just now tried gnome shell again).

The volume/brightness change delay is still happening, but this looks like a different problem as the screen freezes too for 1 to 2 seconds. Described the problem in a new thread: Volume and brighness adjustment OSD delay and screen freeze on Ubuntu 18.04