Please follow these steps if you are having difficulty enabling caller ID on your OnePlus phone:
Go to Settings -> Battery -> Battery Optimization -> Click on Eyecon and choose Not Optimized. Note – on some OnePlus telephones you should choose to keep Eyecon awake all the time.
Go to the Settings menu -> choose Apps -> hit the cog symbol at the top -> Choose Special Access right at the bottom -> click Battery Optimization at the top. If you change the dropdown to display all apps then you can choose which ones will not be optimized in the background. Find Eyecon and choose for it to not be optimized.