Application Error - The requested resource could not be found

We are experiencing the same issue. Did you validated the behavior is also occurring for assystweb? 

IFS Wiki (URL FORMAT) even shows mixed case styles in its documentation which I always thought it was like that for read ability but realized endpoints are truly mixed-case which RFC 3986 Uniform Resource Identifier (URI) says mixing lower- and upper-case letters in APIs can potentially induce errors.

URL does NOT work > https://assyst.XXXX.com/assystNET/

URL does work > https://assyst.XXXX.com/assystnet/

URL does NOT work > https://assyst.XXXX.com/assystWEB/

URL does work > https://assyst.XXXX.com/assystweb

RFC endpoints are case sensitive. What happens if you change the URL? 

Does NOT work > localhost:8080/assystnet
Does this URL work? > localhost:8080/assystNET

Does Not work »  assystNET  (get application error)

Does work » assystnet

Ours is more regarding assystREST is stateless APIs. 

Does not work » assystrest

Does work » assystREST

IFS says, IFS Wiki (URL FORMAT), (Formatted Text markup in assyst) has always and was set up to use REST URLs in that format. 

URLs should automatically resolve to lower-case if entered in upper-case but with Assyst URLs that's not the case. Your issue could be within your “assyst server” configuration (deployment). Make sure in Web Site setup has been all entered in “lowercase” as mixing upper- and lower-case letters in your APIs can lead to misunderstandings and errors as you had indicated.