Could you try following troubleshooting steps:
Launch Reader > go to Edit> Preferences > Page display and change following settings:
1. Use a custom resolution
2. Try turning Off the smooth images, line art,enhance thin lines option .
Let us know if you need any help.
Could you try opening another pdf file using Reader to check if its not a file specific issue?
Also, try disabling "Use page cache" under Edit > Preferences > Page display and check if that helps.
If issue still persists, Would it be possible if you can share the pdf file you are working with to replicate the issue at our end? To share the file here in the forums, refer to the steps given here: How to share a file using Adobe Document Cloud
Thanks for the quick response! It's not file specific. Cleaning cash didn't help either.