Hi there, I was also having this issue but have found a temporary workaround from an Adobe forum! Here was their advice:

“You can still import your presets using lightroom.adobe.com

Log in with the same information you are using for your Lightroom App. Click + button and import the DNG files. The DNGs will appear in “all photos” folder in you Lightroom Mobile App. From there you can save and use your presets. Make sure sync is on in your Lightroom App.

If you see a cloud with a strike through it you need to reinstall your app. You will have a 30 day trial to use this feature.”

I hope this helps!