Drill Pipe backout from TD saver sub and twisted at the connection between HWDP FH and the rest of the BHA at about 5600 ft below

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Drill Pipe backout from TD saver sub and twisted at the connection between HWDP FH and the rest of the BHA at about 5600 ft below

While backreaming out of hole, pumping at 1150 gpm with 120 RPM and max 30K torque, experienced total losses. Regained flow by varying rates to 200 gpm but could not backream out. String could still go down but not up. RPM was then set at 160 rpm and torque limit at 40K, string stalled and could not go up, taking a 100 k overpull. After about 5 mins, Observed string backout from saver sub and dropped into the well.

Fished the string successfully, but in two. One part was string to Jar stand crossover the other part from the HWDP to remaining of BHA. The boxend of the HWDP was seen to have some thread of the jar stand pin indicating a twist off.

What must have gone wrong?

Who has experienced this before?