The issue is that whenever i update worpdress plugins .maintenance file is created in ftp, thats normal thats why when you update the some plugins you see:
"Briefly unavailable for scheduled maintenance. Check back in a minute."
However after 1 plugin does its updates, .maintenance file does not remove itself, and i need login manually to the server and go to htdocs and delete the .maintenance file manually, i tired it chmod to 777 than delete and try update other plugin to see if its removed that time, but no luck, tried also change on wp-config file transfer mode to direct also no luck.
You should also know that you can't update more than 1 plugin at the time since when 1 plugin updates itself that's it you need remove maintenance file and go to plugins again and update other plugin.
I hope i explained the problem clear enough, please do not hesitate ask additional details since i might miss something important.