"Terrain data missing" problem in AUTO

I got the “Terrain data missing” error on AC3.4.2 even with GCS connected through Mavlink Bluetooth interface and Internet available. In the status window “ter_load” is 336, “ter_pend” is 0 so it seems like it even doesn’t request missing terrain.I have the MAXBotix sonar with effective range of 7.6 meters installed (RNGFND_MAX_CM is set to 6 meters). Every time I try to start an AUTO mission with Terrain following enabled, the vehicle does take off, climbs to about the sonar-range altitude (~7 meters AGL - found that out by reviewing the logs) and then failsafe’s with “Missing Terrain Data” error to RTL.from the altitude. Once the vehicle actually takes off and climbs, this is NOT the case when RNGFND_MIN_CM is set too high, I checked this possible issue. It seems like the Fail-safe happens when the copter tries to switch from sonar to pre-loaded terrain data when climbed above the sonar max-range.Any help is highly appreciated! Here is my log file: https://1drv.ms/u/s!AieROjktQIZ3jTu4rVUnWBrObRWH

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