User input is prone to hangs since Tails 4.0
Since I have upgraded to Tails 4.0 from Tails 3.16, I have noticed a new behaviour where user input by keyboard, mouse or trackpoint (this is a Lenovo device) will quite often result in no visible change on-screen, e.g. the mouse pointer will not move or text will not be entered.
NB - The behaviour I am about to describe is present on every normal boot, though it is sporadic, and I have not been able to identify a way of reproducing it. I have not tested Troubleshooting mode, sorry. I have encountered these problems on a Tails install updated from 3.16 and also a fresh clean install.
Keyboard: one striking example is when I used Ctrl-W to close a tab in Thunderbird. The tab did not close, so I pressed Ctrl-W again. Suddenly Thunderbird closed completely, which I thought was a crash, but testing showed that what had happened was that the tab I had attempted to close was one of only two open tabs (a message viewer tab, and the main viewer window tab), and that the tab I had targeted with the keystroke had closed, but the screen had not updated to reflect this. So, when I pressed Ctrl-W again, it targeted the final tab, resulting in Thunderbird quitting.
Keyboard: another example happened while typing this bug report. I paused very briefly in my typing, and when I restarted the text did not immediately appear. I think it did not appear until I typed another character, which caused the screen to update and display the previous and the current character. This behaviour of not refreshing the screen until receiving additional input after the first is common to this issue.
Trackpoint: Response of the cursor to my trackpoint is similar. Interacting with the trackpoint can result in no visible movement of the cursor onscreen, though it will be updated following additional interaction, which means the mouse cursor will suddenly re-position itself to account for the first interaction. This is actually a minor security risk for me because it makes cursor location unreliable and can cause me to initiate clicks in undesirable parts of webpages, for example. This behaviour was noticed at least once during the composing of this bug report.
On at least three occasions, I believe the hangs I’ve described have escalated into full display hangs for up to a minute, where no keyboard, trackpad or trackpoint interaction at all is reproduced on screen, and no automated change is drawn either (e.g. a progress bar will not update to reflect data transfer even though data transfer continues on a hardware level). On these occasions it seems the whole system has hung, but eventually it comes back to life.