I was previously playing a local game in single city mode and have had no issues. I decided to start a region mode game and have two small cities going. However if I research tech and quit after playing the game for a bit, when I reload the app I have to re-research everything. I'm playing on a iPad Pro, latest iOS, latest game update.
I tried deleting the app and reinstalling. That seemed to work for a few days but now I'm back to having lost all my researched tech.
You can see here I am back at the basics needing to be researched but I have buildings built that required research well past what is showing.