There is a column called "Team Member" available in the New UI's "Tasks" tab. Due to a limitation in the number of characters that a particular cell can hold, tasks with large numbers of resources assigned against them, throw an error with code API-1019 in this tab.
This error in the UI is accompanied with an error such as the one reproduced below in the app-ca.log:
ERROR 2018-08-29 05:27:17,113 [http-nio-14001-exec-1] ppm.rest (clarity:admin:5190042__FFACD205-5A01-4B6D-B9FF-BF65C7EFE8D0:PPM_REST_API) ODFObjectMarshaller :: attribute: assigned_resources has an invalid lookup value: [T5003000, T5003009, T5003099, T5003999, T5004000, T5004001, T5004002, T5004003, T5004004, T5004005, T5004006, T5004007, T5004008, T5003100, T5004009
T5003977, T5003978, T5003097, T5003979, T5003980, T5003981, T5003982, T5003983, T5003984, T5003985, T5003986, T5003987, T5003988, T5003098, T5003989, T5003990, T5003991, T5003992, T5003993, T5003994, T5003995, T5003996, T5003997, T5003998]
This issue has been logged as a defect with ID DE43682.
The defect mentioned above is being reviewed by PPM Product Engineering.