When you have more than one donation form on a page and the user starts a donation in one form and then moves to the next the payment element cannot be attached to the DOM due to duplicate selectors.
From Stripe:
The selector you specified (.donation-form-payment-intent) applies to 2 DOM elements that are currently on the page.
The Stripe Element will be mounted to the first one.
Details
When you have more than one donation form on a page and the user starts a donation in one form and then moves to the next the payment element cannot be attached to the DOM due to duplicate selectors.
From Stripe: