I have no solid answer but I do have an opinion. I too get set up first thing in the morning only to find a slow bite for an hour or so and don’t fish much for the evening bite lately. I think that when they shut down in deeper water that they might pick up in shallower areas, maybe a nearby drop off, or on some structure like a treetop or shallower brush pile. I also wonder if downsizing then might pick up a few more. That has worked for me a bunch in the past when they quit hitting regular size baits in the daytime.