your current session has been expired. magento 2

first check for current session life time

php bin/magento config:show admin/security/session_lifetime 

If there is no entry issue the following query

insert into core_config_data (config_id, scope, scope_id, path, value) values (null, 'default', 0, 'admin/security/session_lifetime', 36000);

If entry is there increase the session life time. It can be done in two ways

UPDATE core_config_data SET value = 86400 WHERE path = 'admin/security/session_lifetime';

OR

Issue the following command from magento root directory

php bin/magento config:set admin/security/session_lifetime 86400 
php bin/magento cache:clean

This should solve the problem