I can't pick up items that foxes have previously held. So far the only way I have found to keep the items from despawning is to give them back to the fox. I am not yet at the point in the world where things like hoppers are available to me for testing. I am using forge and optifine and shaders. I'm not sure if this issue will be accepted due to the fact that I am using forge but I thought I would submit it anyway just in case. Killing the fox seems to resolve the issue.

Video: https://drive.google.com/file/d/14HOLYSWXZEzmFnLRbTUr7wUOtitanLhd/view