Thanks for reaching out. We're sorry for the trouble with Adobe Lightroom. I'd love to help you figure this out.
Could you please share the version of Lightroom & the Android version on your device?
The verticle & horizontal sliders respond to the anchor points you use to place a watermark. Please check the anchor point you are using to put a watermark. Please check this image for reference:
This screenshot is from the Lightroom desktop, and this logic applies to Adobe Lightroom mobile (Android) too.
Let us know how it goes.