When opening multiple order guides in different browser tabs. If you Checkout 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)
It can be seen in all the releases
Development team has recommened to use service portal for requestor experience and workspace for fullfiller experience. With Service Portal we are using REST API calls which would ensure that mandatory variables are not missed while submitting the REQ.
Also please be aware to use OOB Widgets to get the complete features.