I think there are a couple of fundamental misunderstandings you have here ...

For starters, Stag Knight's "third skill" is a passive. You can't "activate" it. It triggers upon an ability of anyone on your team being resisted, and places an ACC up buff on them. It has no cooldown, but it will only activate if the ability is resisted - so maybe you've increased the accuracy on your champs, and they aren't being resisted anymore?

When you say Shaman's 2nd skill "often does not increase C rate", are you making a subjective analysis and saying that, despite the buff, your champions don't seem to be landing critical hits more often? The problem here is that 15% is really not a big increase - you'd have to gather quite a lot of data before being able to make a statement like that. More likely than not, you're simply seeing confirmation bias - you're noticing when your attacks are not landing critical hits, and you're not noticing when they are. If you really want to validate this for yourself, take your exact team, and record exactly how often every single ability they use lands a critical hit - I guarantee you it will eventually settle upon the Crit % you see on the stat sheet. Then, do the same analysis with the buff. It should show you that it does indeed happen 15% more often.

The same applies to Elhain. Record every single attack she makes, and I guarantee you it will critical hit as often as her sheet indicates.

All of that being said - something you should be aware of is that critical hits are strongly dependent upon affinity. If you are attacking mobs that are the strong affinity for your champ, you will land critical hits WAY less often. IE, if Elhain (Magic/Blue) is attacking someone like Shaman (Force/Red), you have a very significant penalty to your chance of landing a critical hit. Because she is weak affinity, she has a 35% chance of landing a weak hit, which cannot be critical. Then, after that, she also has a 15% reduced chance of landing a critical hit - which means even if she is above 100% crit rate, she still cannot land a critical hit more than 85% of the time. Combine those together, and you're at only about a 56% chance for a critical hit, even if she has 100% crit rate.

Perhaps you are noticing these reduced critical hits because you've advanced to a dungeon stage where your your damager champions (like Elhain) are now on the wrong affinity?

Oh...I  thought  i  was  hitting  Stag  Knight's  3rd  skill  and  using  it  to  attack  and  thought  he  shot  off  2  blue  looking attacks,  but  I'm  probably  wrong  about  that  after  i  read  what  you  wrote.

As  for  Shaman's  2nd  skill,  I  meant  that  it's  sposed  to  place  15%  increase  C  rate  on  all  allies  for  2  turns  and  the  icon  used  to  pop  up  above  all  my  characters  as  a  buff  but  lately  it  doesn't  every  time.

And  for  Elhain,  I'm  running  really  low  level  runs  to  level  up  low  characters  to  rank  up.  Up  until  yesterday/today  she  killed  everything  in  single  hit,  didn't  matter  affinity.  Mine  is  6*  fully  accended  and  never  had  issues  taking  everything  out  with  her  2nd  and  3rd  skill  on  easy  and  hard  campaign  runs  and  i  run  same  one  over  and  over.  I  could  be  wrong  but  I  just  see  definite difference  in  her  play.

Thank  you  very  much  for  replying!  I'm  only  few  weeks  into  the  game  and  still  figuring  things  out.