Could you provide a read-only link to an example base with some example data please?  (Please make sure there is no production data in there).  This formula seems pretty complex, and having your base to work off of will make it a lot easier to help you test things.  If that’s not possible, could you provide screenshots of the relevant fields please?  

1. Can a record have both a State and a Substate value that clash?  If so, it might be that they’re overriding each other
2. Are {Is approved} and {Has Human Interface Impact} checkbox fields?  If they are, just check whether they’re true instead, e.g. 

   if(
     {Has Human Interface Impact},
     'True',
     'False'
   )

3. Instead of ‘NOW()>{Target Start Date}’, try using ‘IS_AFTER()’ instead - Docs: https://support.airtable.com/v1/docs/formula-field-reference

Hi,

i think you should at least simplify it a bit
 

IF( {Effort Current Total Estimate}=BLANK(),'Scoping',
IF( AND({Effort Current Total Estimate}>'0',{Is Approved}="checked"),'Dev Pending',
IF( AND(IS_BEFORE({Target Start Date},TODAY()),{Has Human Interface Impact}="checked"),'In Design',
SWITCH( {State},
  "Integrate","Feature Complete",
  "Verify","With QA",
  "Closed","Closed",
  SWITCH( {Substate},
    "Nominate","Intake",
    "Investigate","Engage",
    "Fix","In Dev",
    "Review","Feature Complete"
  )
))))

Wow thanks ​@Alexey_Gusev thats super helpful. Im realizing something cant have an LOE be blank then nest the greater than or equal to 1 in the next statement so my order of IF statements nested might be off. Any way to have them in a list and manually rank them in separate if statements?

Im basically looking for the following but getting the nesting wrong. perhaps if I can get help on how to non next these ill just be super specific for each one.

1. If Not Approved and Current Effort Estimate less than 1 = Scoping
2. If Approved and Effort greater than or equal to 1 = Dev Pending
3. If Approved, Effort greater than or equal to 1, and Has Human interface impact checked (equal to one) = In Design
4. If Approved, Effort greater than or equal to 1 use the substate switch then the state switch.
   1. If approved and in state or substate in switch use the stats above.

SWITCH( {State},
  "Closed","Closed",
  "Verify","With QA",
  "Integrate","Feature Complete"
  SWITCH( {Substate},
    "Fix","In Dev",
    "Review","Feature Complete",
    "Investigate","Engage",
    "Nominate","Intake"

  )
)
IF( AND(IS_BEFORE({Target Start Date},TODAY()),{Has Human Interface Impact}=1), {Is Approved}=1,'In Design', 'Error'
)
IF( AND({Effort Current Total Estimate}>1,{Is Approved}=1),'Dev Pending', 'Error'
)
IF( AND({Effort Current Total Estimate}<1,{Is Approved}=0),'Scoping', "error" )

You can set any order and type of IF checks. You can mix blank, GEO 1 and  LT 1
Actually it doesn’t need nothing special, just write them in exactly the same order as your conditions in text.
 

Now, y​​​​our conditions are wrong. (And formula doesn’t follow, even if they were correct, because you inverted the order)
3 and 4 will never be checked, because according to (2), 
If Approved and Effort greater than or equal to 1 = Dev Pending

Another example
“ use the substate switch then the state switch”

means “Check {Substate}, and if “Fix”, type “Dev,  if “Review”, type "Feature Complete"..etc

                      that also means  “if I found match, then it doesn’t matter what’s in “State””

only if SWITCH({Substate} finds nothing from list above, it will check for {State}