Hello,
I have put together a map in ArcGIS Online where I have added a hosted feature layer that is symbolized into three categories based on an Arcade expression I wrote. In the map viewer in ArcGIS Online, the symbols display just fine as shown in the screenshot below.

However, when I load the same map in the Field Maps mobile app on iOS (latest version, iPhone XS), I only see two symbol classes- the tan diamonds and blue dots. The points that fall within the red star category are lumped in with the orange diamonds as well in Field Maps. Screenshot below.

Thanks in advance for any insight on this issue. It seems like a bug to me, but I could be missing something.