Telemetry (hearbeat?) failsafe RTL earlier

Hi there all. I have been using a very old firmware for a while and recently upgraded to 2.78.
I am using the 3DR radios and have flown out to 1.5 km more often than not. Since upgrading to 2.78 my RTL has been triggering at approximately 900metres out in all directions. Very strange as the signal strength is still up near 90%. When looking at the rssi and noise during logs there seems to be no correlation with these figures and RTL being triggered. Transmitter failsafe has been disabled to help with diagnosis, so the only type of failsafe is telemetry based.

Any ideas anyone?

Many thanks.

John Cousins

Providing tlogs and/or data flash logs if they are available will help to troubleshoot your issue.