SQL blocking on p_GrantInheritedAccess stored proc

We are keep on getting SQL blocking on our CRM SQL server, not sure what is going on? could not find anything in our plugins code, used everywhere no-locks in query expressions. checked POA table, looks good.

Let me know if you have any idea what could cause this blocking. appreciate your help..

FYI, We are On-Premise-Rollup 11

blocker_text          :
                              Create Proc p_GrantInheritedAccess
                            @ReferencingObjectId        uniqueidentifier,
                            @ReferencingObjectTypeCode     int,
                            @ReferencedObjectId        uniqueidentifier,
                            @ReferencedObjectTypeCode    int

                        As
                        Begin
                            SET NOCOUNT ON

                        --  For a new entity (Create scenario) ReferencingObjec
                        tId is not shared to any principal yet.
                        -- This check reduces by 50% cost of execution for crea
                        te scenario (no sharing for referencing object exists)
                        if (exists(select ObjectId from PrincipalObjectAccess p
                        oa1 with(NOLOCK) where poa1.ObjectId = @ReferencingObje
                        ctId AND poa1.ObjectTypeCode = @ReferencingObjectTypeCo
                        de))
                        Begin
                            -- Update Existing rows in POA that indicate that t
                        he referencing object was already
                            -- shared to the principals that have share access
                        to the referenced object

                            UPDATE poa1
                            SET InheritedAccessRightsMask = poa1.InheritedAcces
                        sRightsMask | poa2.AccessRightsMask | poa2.InheritedAcc
                        essRightsMask | 0x08000000
                            FROM PrincipalObjectAccess poa1 JOIN PrincipalObjec
                        tAccess poa2 ON (poa1.PrincipalId = poa2.PrincipalId)
                            WHERE poa1.ObjectId = @ReferencingObjectId
                            AND   poa1.ObjectTypeCode = @ReferencingObjectTypeC
                        ode
                            AND   poa2.ObjectId = @ReferencedObjectId
                            AND   poa2.ObjectTypeCode = @ReferencedObjectTypeCo
                        de
                        End

                        -- This check reduces by 50% cost of execution (no shar
                        ing for referenced object exists)
                        if (exists(select ObjectId from PrincipalObjectAccess w
                        ith(NOLOCK) where ObjectId = @ReferencedObjectId AND Ob
                        jectTypeCode = @ReferencedObjectTypeCode))
                        Begin
                            -- insert new rows for principals who were shared t
                        he referenced Object but not
                            -- the referencing Object

                            INSERT into PrincipalObjectAccess ( PrincipalId, Pr
                        incipalTypeCode, ObjectId, ObjectTypeCode, AccessRights
                        Mask, InheritedAccessRightsMask)
                            SELECT PrincipalId, PrincipalTypeCode, @Referencing
                        ObjectId, @ReferencingObjectTypeCode, 0, AccessRightsMa
                        sk | InheritedAccessRightsMask | 0x08000000
                            FROM PrincipalObjectAccess
                            WHERE PrincipalId NOT IN (SELECT PrincipalId FROM P
                        rincipalObjectAccess WHERE ObjectId = @ReferencingObjec
                        tId AND ObjectTypeCode = @ReferencingObjectTypeCode)
                            AND ObjectId = @ReferencedObjectId
                            AND ObjectTypeCode = @ReferencedObjectTypeCode
                        End

                        End
block_program_name    : .Net SqlClient Data Provider