If you run the Gaps in Register by Date report and get the message below -
Go to Admin > Config > Core Set Up > Holidays. In here look for any dates that may be overlapping.
For example;
The Easter and Bank Holiday overlap as they both include 22/04/19.
You can either delete the Bank Holiday and leave the Easter Holiday as it is, or you could remove Easter completely and add the period in again as a new holiday with an end date of the 18th April.