Attitude loss for fixed wing drone by Pix hawk cube 2.1

I need a help in analyzing my drone log file which has crashed down after it lost its height .It is a fixed wing airplane ( V tail ) with DA50 Engine and total mass was about 20 kgs when it was in auto mode the plane made about 15 deg pitch down without command

Please post a log file from the flight.

Thanks Dear for your concern .Please Check the attachment . I have compressed it as it is larger than 25M

(Attachment 2021-01-18 14-34-16.rar is missing)