I'm on OOS 4.0.3, unlocked bootloader, rooted with SuperSU, Magisk installed and with a custom (Franco r12) kernel. Play store is stating that my device is uncertified as well.
My banking app closes itself whenever I launch it, which I'm assuming is because I tripped safetynet. Oddly enough, when I uninstalled and re-installed the banking app, it seems to work now. While I can still update and download free apps on Play Store, I can't seem to buy paid apps. Whenever I get to the payment window and click "Buy", the Play Store app closes itself.
I had all of the above modifications while I was on OOS 4.0.2 and I didn't notice any problems. Purchasing apps worked fine before updating. I'm also getting the DM-Verity message during boot now, which I didn't have before updating.