Another Chun beginner here, you had trouble with the BnB c.LP > s.MP > c.MK xx M.SBK. I did have an issue with it a week ago, but seem to have gotten far better with it.
What helped me was using the Training mode, and switching on the Key Display. First make sure you only do the necessary inputs, Chun Li is somewhat tricky in the sense that you cannot mash the kick buttons. You can’t do it at all or you’ll go to Lightning Legs which can definitely ruin your game if activated unintentionally. (Anybody else think L.Legs should be named No Shadow Kick as per Chinese kung fu terms?)
What I did first was intentionally losing the link after c.MK to just first launch the SBK and worry about linking it later. Once I got it to launch reliably, then I started to work on the execution, and it turned out that it is important that once you start the BnB pressing c.LP and continue to s.MP, at the moment the s.MP starts, you should be pulling down on the stick to start the charging.
The next important thing is to push up and MK at the same time, the key display is very useful here. I tend to lose the link because I’m too fast on the kick button, and if that happens, you don’t see the up-arrow + kick in the key display at the same row. I think the key display showing
up arrow + MK
down arrow + MK
input is also OK provided you didn’t wait too long pushing up.
Courtesy of this forum, a handy way of getting an idea of the cancel timing is to go into V-trigger, do the combo and looking at the animation of m.CK, cancel around the time of the second hit.
After like 5-7 hours of practise, I’m starting to get the combo like 60 % of the time and it doesn’t actually feel that hard any more, so it’s not hopeless. I can now actually expect it to work on Easy Survival (using Double Downs for additional pressure of course). After testing other BnB combo possibilities, I tend to agree the SBK ending is way better than Legs. That knock down is very useful!