Even though a dictionary entry on a task table was deleted, it still shows up on personalize list columns selected/available section.
For example a field called "Test Field 2" was exist on incident table, later administrator decided to delete the "Test Field 2" dictionary entry. So that dictionary entry for "Test Field 2" doesn't exist any more on the database, however, users could see the column name "u_test_field_2" of "Test Field 2" on "Personalize list columns" sections of incident list as shown in below screenshot.
Any supported release.
While performing delete operation of "sys_dictionary" object, transaction possibly got timed out, and hence delete was partial, i.e. column is deleted from database however corresponding storage alias is not removed. Thus resulting in described issue behavior.
When you run into similar issue scenario, please contact HI support via incident with a category "Tables and Dictionary", we will review the situation and fix the issue for you.