This is the only other thing I can think of. Very early this morning there was an update to the Ibotta app. Go to ACCOUNT, SETTINGS. Look at the bottom of the page. You should have version number 6.77.0 or higher. If not, you need to update the app. This should solve the problem. If not, submit a ticket with your TC number to see if customer support can help. Good luck.
I have never encountered issues when submitting walmart receipts. Have you tried restarting your device or removing app then reinstalling it.