Shopping Cart Items Incorrect

The issues I’m having are cropping up here: https://francoiseweeks.com/workshops-in-your-area/ but also exist when adding items from an individual event registration page such as https://francoiseweeks.com/2017/02/botanical-couture-workshop-2/

Here’s the steps to reproduce the problem:

1. Open Chrome browser
2. Clear cookies and history
3. Go to https://francoiseweeks.com/workshops-in-your-area/
4. Click “Add to Basket” on “Portland, OR, February 20 and 21”
5. Correct item appears.
6. Click “Delete”
7. Click “continue shopping”
8. Click “Add to Basket” button on “San Francisco, CA, March 3 & 4”
9. Redirects to shopping cart again,
10. Incorrect item appears in shopping cart (“Portland, OR, February 20 and 21”)

Once this is happening, it’s very difficult to get the correct item to appear. Also cannot add multiple items. Only the original item (Portland, OR Feb 20-21) appears.

Please let me know what I need to do. Thank you!

The page I need help with: [log in to see the link]