It goes like this: I press the shortcut and the caret disappears from the input field for several seconds. Sometimes it comes back on its own, sometimes I have to reach for the mouse to make the input field active again.
Tried various shortcuts. No difference. (Selecting the language with the mouse always works fine, though.) Happens in all apps but most often in Firefox - probably because of its high CPU load. Seems to be a Gnome issue exclusively; KDE switches languages with no weird side effects. Any suggestions?
Are you using iBus? You could try fcitx. I haven't used it myself, but it's very popular in China.