For switch: Press the right stick to open the chat
oh my GOD this worked!! thank you thank you thank you!!!( Since this comes up often, I figured a resource that is easily found and linked could be useful. )
Edit: A new method has been discovered by @BlaDe to fix the results of this bug for all players on all platforms.
Simply enter the "/recountnuts" chat command into the chat box.
On PC pressing T opens it by default. It can also be opened by simply pressing the "/" key which will begin the chat with that keystroke already entered.
On consoles you open the chat box by pressing the right stick.
(The following is the old method for those that can edit their save file.)
When you use the checkup and you get a message reading:
Your savefile is glitched. You have found all the walnuts, but due to a bug (that affects all platforms) it doesn't record the count correctly.
Now, as it says in the subject line here, those who can not edit their save file will need for the bug to be fixed. I am very sorry. This method only works for those that can edit the save file.
First step first: Backup your save file. You can copy the entire folder to another location, edit the original, and if things go wrong after you load it back up, you can replace the corrupted file with the backup and try again.
Next, open up your save file, the same one you click on to get the checkup to work. Search in the text for "goldenWalnutsFound". You'll find a number there, the same one the checkup told you the count was. Change that number to 130.
Use the checkup again. Fixed? If not, you can ask for help.