We're sorry about the trouble with Lightroom mobile. Would you you mind sharing the version of Lightroom mobile you're using along with the version of Android you're working on? What's the make & model of your mobile device? Did you start experiencing this issue after the latest version? Do you experience the same behavior with a different graphics for watermark?
If you're using the application through a subscription, you can try re-installing the application to check if that helps. Please go to Lightroom.adobe.com to ensure that your images are synced & backed up prior to re-installing the application.