Dexcom CGM. Need some advice.

I haven't experienced any issues with the trend symbols disappearing. I did get a notification on my phone that they were still testing the app for the iPhone 6S. I'm not sure if you also have a 6S, but that may be why you're having issues.

To address your second concern, there have been several instances (and especially with a 1-2 day old sensor) where the readings were considerably off from finger stick readings. I've noticed that entering in one calibration value will partially adjust the reading. However, entering in two calibration readings will adjust it entirely. I assume Dexcom does this to account for standard glucose monitor margins of error.

Example: if my Dexcom says I'm at 100 and I enter in one calibration value of 80 it may adjust to a reading of 90 (I'm in the USA).

However, if it says I'm at 100 and I enter in two calibration values of 80 each, it will fully adjust to 80.

When no arrows appear it means the sensor can not calculate how fast your blood sugar is raising or falling. You also have to remember there is a 20 minute time lag between sensor and finger stick reading.