Hello again Leandro,
Another user has potentially discovered the cause of the slowness during login: check to see if you have the "Check for updates" setting enabled - if so, disable it.
This setting, when enabled, will normally ping the Artefactual AtoM release servers to check to see if an AtoM release exists that is newer than the current installation. If yes, then upon login a banner is displayed with a link to the Downloads page. See:
I am not sure if the issue is that our servers have been slow, or if there is a bug or regression in how this check is implemented in AtoM's code, but
according to this forum thread, disabling the check should help resolve timeouts and/or slow loads during login attempts.
Meanwhile, we will continue to investigate this and hopefully address it in a future release. Hope this helps!