The default theme doesn't work. To be exact, the logo does not show even though .png file is in the correct folder.
I used to use shift+F5 to show the latest image. Is that correct?
What is the permission of your images folder?
If you try to manually access the logo image using URL, does it load?
If you want to reinstall default theme, you can create a default theme by following steps -
Go to Templates and Settings -> Themes -> Create New Theme > Give a Name to the theme and select MyBB Master Style and Create.
In your case, I think the issue is probably with permissions.
eh, while such may not pertain to your current issue, figured I would still mention this just in case you need the real step by step directions on how to completely recreate the default theme, say for example if it was removed by a plugin (as such is completely possible to do as history has proven, lol) or whatever reason, as in such cases the previous suggestions would not work, anyhoo I wrote instructions to create such a "savior file" a while ago (ie: 2016 => 1809) for another user having the need for such years ago, ie:
https://community.mybb.com/thread-206870...pid1257270