Hi,
We're sorry about the trouble with Lightroom mobile. Would you mind telling us if you are using Lightroom mobile through a subscription or are you using the free version of the app?
If you are using the free version of Lightroom mobile, the images & presets are saved locally on the device & not synced to the cloud storage or across devices. In this case, you would need to export the presets from the previous device & import them to the new one.
If you are using the app through a subcription, please go to Lightroom.adobe.com & select an image to edit it. Then check under Presets to see if you are able to see the presets there. Also, you can check out: https://feedback.photoshop.com/conversations/lightroom-mobile/lightroom-mobile-new-update-presets-gone/60c757ca3d4e7d4b735484ae
You might be experiencing this due to a recent change.
Regards,
Nikunj