"Missed" history is not getting shown in chat window
When opening a new chat window, Gajim is able to show the last lines from the history. But when a chat window is already open and Gajim somehow misses some messages (due to missing network or a computer in standy), it won't show the missed messages in the chat window. They can be seen in the history, so they are getting correctly synced from the server.
When reconnecting an account, Gajim should (if enabled) update the chat window and show the missing lines from history. I think this a common problem with laptops, which will often be sent into standby during conversations, which will continue otherwise, for example on mobile phones. Back on the laptop, you have to manually look in the history or reopen the chat window to see those messages.