It sounds like this issue. The scaling of the PDF attached as an Xref changes in AutoCAD 2023 and later (autodesk.com) As with all things, recommend latest updates.
Quite frankly if I was upgrading I would recommend Civil 3d 2025. I have been testing it by opening 45 Civil drawings and I am seeing significant performance improvements. I haven't tested with Civil 3d 2023 but time to open all these drawings is:
Civil 3d 2022 419 Seconds
Civil 3d 2024 360 Seconds
Civil 3d 2025 280 Seconds
I hate waiting for drawings to open so being able to reduce that is a big win for me.
Check out my Civil 3d blog at: http://c3dk.com/
Favorite Posts: Use Dynamo For Surface Analysis: https://youtu.be/eJNdX6guMP8
Fast Track your site grading with the new Corridor Workflow: https://youtu.be/Gg7u9-LgIL0