Marginal Redness and Bleeding following Definitive Crown: Ideas?

I have been doing quite a few extraction and immediate implantation cases with socket preservation using collagen followed by immediate fixed implant provisional. I normally do this for upper incisors or upper premolars. Most of these extracted teeth have acute or chronic peri-apical lesions. Once done, It all goes very well and after 3 – 4 months I switch to a porcelain crown. I have noticed that on 3 cases of mine there is redness and some bleeding developing around the buccal margin. At first I thought there might be a different fit of the porcelain crown to the provisional acrylic crown leaving a space, so I added porcelain to maybe fill the gap and tighten the fit at the gingival margin. But, the bleeding persists. There is no swelling or pain, just slight bleeding. The hygiene is otherwise good. Can™t make heads or tails of this. Any ideas? Many thanks.