Generating too many transient options

Hello, dear team,

You plugin works perfectly and extremely fast. But, when I looked to the database today, despite of I have only 600 users registered I saw 40 000 of transient options generated by Nextend(The only Nextend plugin I am using and ever used on that website is this one). And they clearly will not be deleted even if they are expired as not second call has done to them. I can use some tools to clean them, but isn’t it much weight for such little amount of users? Can I stop this happening from setting of the plugin.

I would appreciate if you can explain in what purpose they are used and can be eliminated or reduced. Example rows of the options:

(3631642, '_site_transient_timeout_nextend58758e3aaefcc9.94469841_fb_r', '1484102730', 'no'),
(3631643, '_site_transient_nextend58758e3aaefcc9.94469841_fb_r', 'http://sitename.com/post_type/post_name', 'no'),

Thank you for your time!