It hangs up going between screens and even stutters scrolling sometimes. Its forgotten how to do widgets and I cant add them anymore. If I turn night light or grayscale on the colour shifts but doesn't go back if I turn it off, requiring a reset. A few other things... Should I reinstall it? Is there a chkdsk or malwarebytes type program I can use? Is it possible to reinstall the original pixel OS?
This would be my guess too. Weird things happen if files are left behind by the old OS. Otherwise they should be able to reinstall it, or the stock ROM using the instructions on the website.
Those are strange issues, I personally haven't experienced any of them.
If you're interested in malware detection, you might try Hypatia.
A reinstall might be helpful, but if you'd like to go back to the original Pixel firmware you can do that pretty easily. First, go to this GrapheneOS installation page and scroll to the bottom for the instructions on removing the non-stock boot key. Then you can use this link to install the stock firmware: Google web flashing tool. It uses a similar web flash tool to what graphene uses for installation.