Can you give more details on how you got into this state:
Are you editing the default tilesheet that was created at project initialization, or another image?
Do you have the image opened in another software?
Did you made any changes to the project settings?
Can you open the developer tools (View > Toggle Developer Tools) go onto the "Console" tab if not already selected, and tell me if you see any logs or errors in there?
So, I am editing the default tilesheet, I haven't opened it in another software, I created a new project with unedited settings to see if the problem still occured, And no there aren't any errors in the console.