I'm not sure whether its hardware or software problem, but as I have reflashed software and reset the device multiple times, I suspect hardware. Here are the symptoms:
After successful flight i tried to connect APM via telebee radio. Telebee's didnt link, so i brougt the usb cable. On mavlink conncet it reads all params up to "got AHRS_RP_P" and then the reading stops, until it gets the timeout. the detailed error message is "got 224 out of 256 params in 6 retries".
I tried flashing the software- overwrite my arduplane 2.68 with arducopter 2.91, then installed again the arduplane firmware. The error remains the same.