When a user submit a query to get records from a table based on dates, the result differ depending on whom submitted the query
Users are in different timezone
This is occurring when users are part of a different timezone set in the sys_user record. This is expected as different timezones might include different records when accounting for the very start or very end of the month depending on the number of hours from other user in a different timezone. You can test it by changing the user's timezone to match whatever the other affected user is.
For example, if you are looking at a report that is the whole month of June it means the differences will either be on the first of the month (June 1st or the last of the month (June 30).