I was using FIleMaker Pro to serve files to my iPhone for testing and the results were terrible. The iPhone kept dropping the connection, etc.
A lot of people use FileMaker Pro to serve a few clients rather than invest in Server and perhaps they are experiencing the same problems in house.
Symptom: after a bit the iPhone loses the connection, freezes, etc.
Cause: I was using the WiFi router of the motel which has a 50 MB Comcast connection which works great for surfing and videos and WPT tournaments. Not so good for FileMaker Pro.
Solution: I switched to my own WiFi router ( a T-Mobile mobile hotspot ) with a closed network and not connected to cellular. This works just like a plain vanilla router.
Now everything works like it should and the iPhone stays connected and even works faster with finds sorts etc.
Reason: the connection signal with cable connection has a ping type delay which can be short or long depending upon time of day and network traffic. This delay can affect the performance. Next, if there is a delay and sometimes I don't use the iPhone for 10-15 minutes, Comcast and other providers will drop the connection and reconnect as if you were reading a web page and then later opened a new one. FileMaker doesn't like this for several reasons such as getting a new ip address. I also guess that the iPhone and laptop exchange messages in order to keep the connection active and the dropped connection interferres, etc. Of course the explanation could be different, but I don't care. I solved the problem.
Summary: if you are using FileMaker Pro to serve local clients, use a dedicated WiFi router or hub rather than using a WiFi router that is surfing the Internet.
I'll mark it as a question if anyone wants to comment. I solved my own problem (again for the 1000th time).