ajuhos
Hi
In older version to new version to main change will be in the message as previous message system will be replace to Chat system and your message will not show instant as it will be new chat and previous message come later when cron job run each time.
Kindly use recommended system settings : https://documentation.jomsocial.com/wiki/System_Requirements
Now start the update one by one and try 4.5 version.
If still there is issue, kindly edit fields in first post and submit temp super user login.
Do not try the migration on live site or without a full backup.