Issue on email report

Hello,
I have a issue with WP Statistics, if i add to the yestarday’s total visits the yestarday visits they are different of today’s total visits.
Do you know why?
Resources
Memory usage in PHP: 16.912.608 Bytes
Memory usage in PHP

PHP Memory Limit: 768M
The memory limit a script is allowed to consume, set in php.ini.

Number of rows in the wpvo_statistics_useronline table : 0 Rows
Number of rows

Number of rows in the wpvo_statistics_visit table : 146 Rows
Number of rows

Number of rows in the wpvo_statistics_visitor table : 647 Rows
Number of rows

Number of rows in the wpvo_statistics_exclusions table : 0 Rows
Number of rows

Number of rows in the wpvo_statistics_pages table : 2.463 Rows
Number of rows

Number of rows in the wpvo_statistics_historical table : 0 Rows
Number of rows

Number of rows in the wpvo_statistics_search table : 541 Rows
Number of rows

Version Info
WP Statistics Version: 12.3.6.1
The WP Statistics version you are running.

PHP Version: 7.0.30
The PHP version you are running.

PHP Safe Mode: No
Is PHP Safe Mode active. The GeoIP code is not supported in Safe Mode.

PHP IPv6 Enabled: Yes
Is PHP compiled with IPv6 support. You may see warning messages in your PHP log if it is not and you receive HTTP headers with IPv6 addresses in them.

jQuery Version: 1.12.4
The jQuery version you are running.

cURL Version: 7.59.0
The PHP cURL Extension version you are running. cURL is required for the GeoIP code, if it is not installed GeoIP will be disabled.

Zlib gzopen(): Installed
If the gzopen() function is installed. The gzopen() function is required for the GeoIP database to be downloaded successfully.

GMP PHP extension: Installed
If the GMP Math PHP extension is loaded, either GMP or BCMath is required for the GeoIP database to be read successfully.

BCMath PHP extension: Installed
If the BCMath PHP extension is loaded, either GMP or BCMath is required for the GeoIP database to be read successfully.

File Info
GeoIP Database: 3.2 MB, created on aprile 27, 2018 @ 8:17 am
The file size and date of the GeoIP database.

browscap.ini File: browscap.ini file does not exist.
The file size and date of the browscap.ini file.

Browscap Cache File: Browscap cache file does not exist.
The file size and date of the Browscap cache file.

Client Info
Client IP: 78.13.109.98
The client IP address.

User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36
The client user agent string.

Browser: Chrome
The detected client browser.

Version: 66.0.3359.181
The detected client browser version.

Platform: Windows
The detected client platform.

regards Carlo