No 'Aswer' button visible with Twilio & Zoho

No 'Aswer' button visible with Twilio & Zoho

My calls from Twilio are directed into Zoho CRM and are intermittently working. Occasionally I get the pop up to say somebody is calling, but there is no 'Answer' button and sometimes the calling box shrinks to just display "Calling..." which remains even after the caller has hung up. Anyone experienced this? I'm on a Chromebook if that matters.