I can edit Wikidata on mobile (all I've done so far is descriptions), but tapping the save button goes to the desktop site with "Sorry! We could not process your edit due to loss of session data." On Wikipedia I usually get this message if an edit takes a long time (i.e. long delay between starting the edit and clicking "save page"), but here it happens every time. Tapping the desktop site's save button then works and sends me back to the mobile site.
T108683 may be related.