I have documented a particularly bad case of bumblefoot from an EE this year. I was thinking about creating an article about it. I think I will, because it could be helpful to others here. The one case was puzzling, because there was not a clear core, or scab. I believe the cause was a small pine needle that had punctured her foot.
A puncture sounds like a good diagnosis, and/or maybe a piece of a pine needle broke off inside the foot pad sort of like a small splinter? I'm a worry wort and overthink diagnosis but IMO a good thing to overthink. For illness/injuries that don't show improvement within 24 hours, I go to the vet as a precaution because usually by the time a bird shows stress she's been hiding the condition for a while before we as humans notice it. A 100-lb dog or 150-lb human can suffer a few days without terrible consequences but a little 5 or 6-lb chicken will succumb quickly and needs immediate attention so I never go more than 24 hours if one of my birds doesn't show improvement after treatment.