Second Transfer attempt goes to dead space

I am the receptionist for our company using a Yealink phone in conjunction with the RC desktop app. We have always used warm transfers. A call comes in on the general line asking for User 1. I hit the transfer key and then User 1's extension. I can hear it ring. If User 1 does not pick up and the voicemail begins, I end the transfer and speak to the caller. I alert the caller to the fact that I will transfer them to voicemail (since they have the option to speak to another rep). Here is the problem: When I begin the second transfer by hitting the transfer hot key, the caller is immediately transferred into what seems to be dead space or they are transferred to User 1's voicemail without the announcement resulting in a long voicemail with just background noise or conversation. Is this a setting issue or user error? Thank you!