This happened to me on iOS.
Obsidian Mobile version: v0.0.15
Apple iPhone 8, iOS 14.4
Sync method: Obsidian Sync
I do not open Daily Note on start-up.
I first opened today’s daily note on mobile. I do not have the templater plug-in installed, so the daily note was not filled out correctly.
I switch to desktop and opened the daily note. Templater correctly replaced template tags with the right data. I spent several hours entering contents into the daily note.
Later, I opened the daily note on mobile, and it upended the daily note template at the top of the existing daily note. The template tags were not replaced, as expected. All of my previous daily no contact appears below the daily note template.