Updates to Camera Raw, Lightroom Classic, and the Lightroom Ecosystem were released yesterday evening and contain a fix for this issue. Please install the appropriate update and see if it solves this problem.
Adobe has rolled out version 5.4.1 of Lightroom mobile for iOS and iPad OS. This release resolves an issue introduced in 5.4.0. As a result, functionality such as new camera support, additional language support, and bug fixes are not available in 5.4.1. We will issue another update to bring that functionality back soon.