The WI under an ECC3 contract introduces a requirement for the PM to accept a Contractor’s proposal before a subcontract tender enquiry can be issued. If clause does not state any grounds for the basis of rejection (as per the programme or subcontractor rejection grounds) and the PM rejects the enquiry, can this be notified as a CE under 60.1(9).
It is not at tender enquiry that this provision applies. Under clause 26.2, it is when the Contractor submits the name of his chosen Subcontractor to the Project Manager for acceptance.
As with all clauses governing acceptances by the Project Manager, a reason is stated in this clause for non-acceptance and there is the more general reason for not accepting as per clause 13.4 i.e. more information is needed.
As you point out, clause 60.1(9) is a compensation event if the PM “withholds an acceptance … for a reason not stated in this contract.” If the PM does not given a reason, then they haven’t given a reason stated in the contract i.e. in my view it is a compensation event.