I recently added a second Lowrance HDS-12 unit to my boat and now have issues on both units with the Structure Scan. Here is my issue;
When I set the range for left and right to any amount (40, 50, 60, etc), within a couple of minutes it will automatically jump to 200 or 300 feet on each side. I don't have it on Auto. I�ve tried both units on 455 and 800 khz, plus one on each. Same results.

I have the transducer connected directly into the console HDS 12 unit. If I turn the bow unit completely off, the console unit works fine. Both units have the latest software patches and have been reset to factory default and setup again. Still get the issue.

Any ideas as to the issue and any possible fix would be appreciated.

If you don't get your answer here, try it on the low forum at bassboatcentral.com

Do both units have current software

Both units have the most current software version.

I called Lowrance tech support. The issue is only when you have two HDS12s; they both want to be master instead of one being master and the other a slave. They said it is a known issue and they are working on a software update to fix the issue. No ETA on the fix though.

I have the HDS7 Touch and a HDS Gen2...and it does it with them sometimes too. I have to turn the main one off and turn it back on then it usually fixes itself. But I noticed that every time I switched to 450 it would switch back to 800 on its own.