Why do messages update slowly onscreen?
This occurs when the program is set to “Show Messages” and the message file is getting overly large. A workaround is to turn off the display of messages (choose Settings | Show Messages or use the keyboard shortcut “Alt-S, S”), scroll to the desired date, then turn the messages back on again. Versions after 3.9.8 offer improved performance when scrolling through dates with a large message file open.