This issue happens if the window is resized while the "Tools", "Code" or "Console" tab are open. Going back to the "Textures" tab leaves some textures off screen. Only way to revert this is by closing and reopening MCreator, but it's possible to reach those textures by using arrow keys.
MCreator issue tracker has been migrated to GitHub.
Existing tickets have been migrated to GitHub. Please open new tickets on the GitHub tracker instead. If you do not have a GitHub account, all feature requests and bug reports from forums are still considered and checked by the maintainers.