In the top left four boxes of my inventory, I'm no longer allowed to select and move whatever's in there, into my hand to use or even just replace the spot with other items. I've tried saving and closing the game all together, but the issue still persists.
Thank you for your report!
We're actually already tracking this issue in MC-143776, so I resolved and linked this ticket as a duplicate.
If you would like to add a vote and any extra information to the main ticket it would be appreciated.
If you haven't already, you might like to make use of the search feature in the future to see if the issue has already been reported.