My experience is with cornmeal. I found that on humid days, the cornmeal absorbs the moisture from the air and clumps in the spreader preventing an even flow. I worked out a way to bounce the spreader and it applied just fine. It turns out spreaders are not built to be bounced, so it only lasted a season. You might want to rent a spreader.

I’ve needed to bounce spreaders too.

For cornmeal, did you use broadcast spreader or drop spreader?

I have used both a drop spreader and broadcast. The drop spreader is the one that broke.

Did the broadcast spreader work satisfactorily (without significant clumping, or much fine soybean ”dust” that drifted elsewhere rather than being applied to the lawn)?

I realize environmental conditions could play a role in either, or both.

I ended up using a broadcast spreader. It worked fine, I started with a half open hopper setting, but the meal dropped so quickly that alot was applied in just a few steps, so I reduced the opening size considerably. No clumping. No bouncing needed. A tiny bit of dust, and there was some wind, but close to all of the meal went where I wanted it to.