Hi all I’m having strange issues with my sounder, wondering if anyone has had similar or any ideas…

All was working perfectly since I installed but last two trips it won’t read properly when stationary. Initially encountered the issue when fishing deep but also have the same problem in shallow water.
Didn’t take any photos unfortunately!

If stationary, it’s almost like signal is interrupted at regular intervals as will show ground with tiny vertical lines.
If idling forward it works fine.
No change if motor is running or not
Transducer hasn’t moved/dislodged at all
Traveling at speed is also worse, used to get clear reading at 20+ knots, now still reads bottom but nowhere near as clear.
Any ideas?