Users are seeing that their list layout configuration has changed unexpectedly. Columns the user does not want to see are now displayed or fields the user added to their list layout have disappeared.
This can occur in all releases
There are multiple list layout records for the Incident table in the Default view where the User field is empty. Having multiple system default records can cause the platform to get confused on which is the actual Default list view to use and could randomly reset a user's personalized list as a result.
Usually, a list layout record will have a user name associated to it, identifying that for a specific view, this is the personalized column configuration on a table for this individual user. There can be several list layout records for the same table with different user names, as each user has the ability to personalize the columns that are displayed as they see fit.
When a list layout record has the user field empty, it means that this is the system record to be used for the specified view by all users. Each individual view can have a system default layout record for every table.
If a customer is on an early Geneva patch, they might experience their list layouts reverting to those of users who have the same roles. This is a separate issue and has been documented in Known Error KB0584506 (https://hi.service-now.com/kb_view.do?sysparm_article=KB0584506).