The contract does not give the PM discretion over whether or not they issue an instruction i.e. clause 19.1 does not say “may give an instruction”. I’m not sure why there was uncertainty surrounding contractual procedure, clause 19.1 is very clear about what needed to be done, as are the compensation event procedures. In any case, the PM’s argument is pretty weak, they should have issued an instruction, even if that was just “carry on as best you can”. The PM had no obligation to issue an instruction telling you to stop or not to start which is probably what you were looking for however if the effects of COVID-19 meant you effectively came grinding to a stop anyway then your costs and times should be recoverable under clause 60.1(19). Note how this compensation event does not make mention of the PM’s instruction so it doesn’t matter that you didn’t have one, provided the event passes all of the other tests.
Unfortunately if all else has failed e.g. direct negotiations with the Employer then the only recourse the Contractor has is adjudication. You could try a strongly worded letter from an independent third party as a precursor.