Project Manager can not access a custom field (API-1007 error) created on the Investment object using the Modern UX security set up Field Level Security (FLS), with Edit and View access rights granted.
Release : 16.1.0
Upgrade to 16.1.1 from 188.8.131.52 and now same user was seeing API-1007 error can't reproduce the API error message popup from the the projects grid view in 16.1.1, and can update the value of the attribute lookup with Field Level Security enabled on it. The issue is fixed in coming Clarity 16.1.1 version due in March.
Please check Clarity SaaS upgrade schedule.