When opening multiple order guides in different browser tabs, if you check out one of the order guides, the most recently opened Order Guide will be submitted, regardless of whether you had filled out mandatory details.
(e.g. Open Order Guide 1 and do not checkout, Open a second order guide in a new tab, Go back to Order Guide 1 and fill in details and checkout -> order guide 2 will be checked out with no values filled).

The issue is not reproducible on demand but we have identified a pattern which may trigger it:

1. Open an Order Guide
2. Fill out variables for some catalog item but do not check out yet.
3. Open the same order guide in either different browser or incognito window
4. Follow the steps and checkout the order guide.
5. When the order guide is checked (#4), it sometimes checks out the item from (#2).

After carefully considering the severity and frequency of the issue, and the cost and risk of attempting a fix, it has been decided to not address this issue in any current or near future releases. We do not make this decision lightly, and we apologise for any inconvenience.

It is recommended to use Service Portal for requestor experience, and platform native UI for fulfiller experience. Service Portal uses REST API calls, which would ensure that mandatory variable are not missed while submitting the REQ. It is also recommended to use OOB Widget to get the complete features.