This may be happening because the delivery method options for eTicket is set to immediately upon completion of order. Try changing that setting to email upon completion of order. Follow the steps below to change that setting: 
  1. Click tickets > Delivery methods
  2. Click the arrow next to eTicket and click edit
  3. Change the option in the tickets field to email upon completion of order
  4. Go back to the order
    1. Click sales > order search 
    2. Search for and select the order
  5. Click on the Tickets tab on the order record
  6. Click on the email to resend the eticket email
If you don't have eTicket listed as a delivery method for Online Sales, you won't have the option to manually send an eTicket after the order is complete. If you would like to add eTicket as an option for Online Sales moving forward, follow these steps:
  1. Click Tickets > Sales Methods
  2. Click Online Sales
  3. Select the Delivery Methods tab and click Add
  4. Select eTicket from the drop-down and Save