We're currently tracking an issue where the manager still does DNS lookups at 7.5 despite being configured not to do so. It sounds like that is what you are running into.
There is a database option that can be disabled by manually logging into MySql and executing the below command:
mysql -uroot -p lf
update iv_emsproperties set value='false' where name like '%iv.dnslookup.realtime.lookup.enable%';
We have seen it cause issues with alert processing on the manager, which is likely related to your other query.
Thanks about the this information. Very important!
I´ll execute this command and after that, take a loot at ems.log.
And i´ll check about the other issue too. (Error Notifying Update)