Thank you for your question about what insect is eating your plants. From your photos and description of the damage, I believe the insect is a root weevil. The adults feed on the leaves at night, which is why you are not seeing them. Following is source that provides a description and management methods for root weevils: https://pnwhandbooks.org/insect/hort/landscape/common/landscape-root-weevil

The Deschutes County OSU Extension website provides more information about common insects found here in Central Oregon:   https://extension.oregonstate.edu/gallery/common-insects-found-urban-landscapes-central-oregon

If you need additional information, I encourage you to call the Deschutes County OSU Extension office in Redmond at<personal data hidden>. You can ask to speak with Amy Jo Detweiler or Toni Stephan, members of the Horticulture Staff. Both Amy Jo and Toni welcome your home garden questions and are happy to talk with you.