I have a Siglent SDS1104X-E, and I'm trying to debug an issue with an LED driver. I was probing the switching node of the driver on one channel and the PWM'd output of a transistor driver that shunts the output to ground to control the brightness. The scope probes ground clips are connected in two different spots, specifically to two different mounting holes on the board that are connected to circuit ground. I've tried reversing them and attaching them to the same spot to see if it would make a difference, and it did not. I've noticed that when I probe only the PWM signal, I see what I expect: a square wave between 0 and 12V.
However, when I am probing both the transistor driver output and the switching node, I see this:
Changing the trigger channel doesn't make a difference, I still see what appears to be the signal on channel 1 bleeding into channel 2. Is this normal? Is there a way to prevent it happening?
 After further experimentation, I've found that I can greatly decrease the amount of signal bleed by removing the hookup wires that I had used to attach the ground clips to the ground points, and just clipping the ground points directly. I'm still a bit puzzled as to why the length of the ground lead would have this effect.
[edit 2] Here are two additional traces. In the first, I attached the ground clips directly to the mount points on the board, which are attached to a (shared) circuit ground.
The second trace is from a few minutes later, after I shut off the device and then powered it up again. The ground traces are short as from before, but the signal bleed is back.
Here is an image of the probing setup. The grounding points are circled and red, and the two probe points are inside the green circle.
Here are some images of the full board layout, and a closeup of the driver portion (of one of the drivers). Just for context, there are three drivers on the board, but I only have one active for this test (the center one, which drives the green LEDs). The other two are disabled via the EN pin (the drivers are LM3409s). I've also added a schematic for the drivers.