Last night the CognisantMD team released a workaround for this issue, which appears to restore the primary provider restriction behaviour for clinics. As a result of this workaround, clinics may find that their online booking is working again.
TELUS continues to investigate the original cause of the problem that led to the primary provider not being returned in some circumstances from the TELUS API. However, the result of this investigation is unlikely to impact clients, now that the functionality has been restored.