Emulator

What's the problem? Describe what went wrong.

If Dolphin (or a game via OSReport) spams log messages, some log messages will be dropped.

What steps will reproduce the problem?

Load up a game with something spammy (maybe DVD Interface) enabled. Compare the log output between a file/stdout and the log window. Some lines will be missing.

Which versions of Dolphin did you test on? Does using an older version of Dolphin solve your issue? If yes, which versions of Dolphin used to work?

Honestly, I don't know. This probably may be present in every single version of Dolphin to date.

Looking through git, I found that log line dropping was added 8 years ago: https://github.com/dolphin-emu/dolphin/blame/400a737ef95dc5d8441d5a70850c558bf7b3f302/Source/Core/DolphinWX/LogWindow.cpp#L342

Maybe even more, since before then line dropping was commented out prior to that commit. You get the gist, I'm not going to dig any further.

Perhaps instead of dropping, the LogWindow could have a maximum amount of lines.
For each update interval, the lines that are in the line buffer are rendered.
Adding new lines would remove the earliest line _visible_, not the earliest line _queued to be visible_.
I don't have any experience with Wx so I'd rather not touch the code... Also compiling Dolphin from source isn't very fast (for me), I blame Wx.