I have had similar issues with my sonars. Usually goes haywire in heavy weeds, no correct that, weeds of any thickness. Especially if I am sitting or slowly drifting.
Moving out of the weeds takes care of it most of the time.
I have never done it, but have heard you can order a transducer directly from airmar with Lowrance connectors on it, spendy though, the number that comes to mind was around $800 I am prolly way off though.
Like Nick said, it feels like a “software” issue. Like not enough computer power to process all of the returns from the weeds. The software updates were supposed to address this, I have held out with my original software version, not wanting to use “beta” versions in 3 grand worth of sonars.
I have a dead one now anyway so I may end up with the newer version of the software in one of them when/if it gets repaired or replaced.
My first sonar was a 332c that never missed a beat. I could be sitting in 3 fow on top of weeds so thick you could not see bottom and it would keep chugging along. I hated the small screen though and moved up to a 113 and a 37. Have had the 113 replaced 2 times and now the 37 just died on me last week. Gone through 3 transducers in that time. The ONLY thing that has continued to work for me is my LGC-2000 gps antenae, have heard headaches others have had with them, I must have lucked out with a good one.
If you have the shallow water option you could try that, I have not seen a difference personally while using it but I do leave it set to that mode.
Good luck, not sure what else to tell you.