2 separate issues going on here ...
The last one at 10mph is turbulence coming off the boat hull creating bubbles which show as dark vertical lines in DI ... Remedy for this issue is slow down below 10mph ...
The 1st issue does "look like" jack plate echoes ... But seems odd as disappearing ... Verify this possibility by temporarily mounting the xducer to a board and stick it farther down in the water to see if the echoes in the image go away ...
Rickie