Issue hooking mstsc.exe on windows 10 1903

[rajiv2790]

I compiled the DLL (RdpThief.dll) and injected it into mstsc.exe process. It is able to hook ADVAPI32!CredIsMarshaledCredentialW but is unable to hook SSPICLI!SspiPrepareForCredRead and dpapi!cryptprotectmemory. I was able to verify this by attaching a debugger and looking at the assembly. Only the CredIsMarshaledCredentialW function has jump into the loaded dll. Any pointers on how do I debug this issue or have you encountered this before?

Are some DLLs immune to hooking?