A user reported this. I was able to reproduce it with Reaper and Bitwig with our plugins. Our plugins are using 8.0.10 with standard Ubuntu Linux.
The plugin does not forward space, esc, and probably other keys in Linux when the plugin UI was clicked and has the focus (send all key inputs to the plugin in Reaper disabled). I need to click the DAW Window and remove the focus to start/stop the sequencer with the space key, for example.
The same plugins forwards those keys on macOS and Windows. I would expect that this works the same on Linux. It slows down the workflow for users when this does not work. Some non-JUCE Linux plugins seem to work.
Any fix or help would be welcome.