That was known issue in Joomla which this issue still persists on 3.7.2.

Can you try download my attached file and replace into this following file location and see how it goes?
JoomlaFolder/libraries/joomla/filter/input.php

You have to backup the original file first before you replace the file.

Reference link : http://www.itoctopus.com/saving-articles-timing-out-after-updating-to-joomla-3-7-read-this