Some plugins like "YOAST" conflicts with ShareThis WP plugin and doesn't allow them to appear on the posts.
We have escalated this to our Engineering team. They are working on priority to resolve the issue and will be fixed soon.
For now, here is a workaround -
If you have installed "YOAST" plugin on your WordPress site then -
Please update the sharethis settings for wordpress from here:
Yoast (Shows up as WordPress SEO once installed)
Under "Social" ---> Facebook tab ---> uncheck "Add Open Graph meta data"
Under "Social" ---> Twitter tab ---> uncheck "Add Twitter card meta data"
and then Save the Settings.
Thanks for your patience and for using ShareThis!