When the Launch URL blueprint node is used to open a link on an iOS device, any question marks in the URL are converted to %3F instead and invalidate the link. This is different from the behavior on Windows and Android, where the question mark stays intact.
Please note: The device needs to be connected to the internet, even if the link isn't a real link, to see this behavior. It also does not seem to be device specific.
This also occurred in 4.12.5
Head over to the existing Questions & Answers thread and let us know what's up.