Hello,
Adobe Analytics (AA) uses the IAB (Interactive Advertising Bureau) list of spiders and bots by default.
In addition, AA also allows bot filtering at the user agent level & custom IP addresses.
Navigation Path - Analytics > Admin > Report Suites. Select the correct Report Suite, and then go to Edit Settings > General > Bot Rules.
Reference document link - https://marketing.adobe.com/resources/help/en_US/reference/bot_rules.html
Huge discrepancy being seen in GA sessions v/s AA visits may be because of various filters set-up in GA reporting view. Also, check if session timeout settings for GA Property in Admin console has been changed from default value of 30 minutes. In AA, by default, visit ends after 30 minutes of inactivity & can be shortened for a report suite if specifically requested, but it cannot be lengthened.
Let me know if this helps out.
Regards,
Saurabh Kumar.