Group admins are permitted to (provided they operate their group within the terms and condition) delete users, posts, images etc. if they wish.
If you wish to censor or restrict posts in your group then you are permitted to do this as what they call 'admin'.
If you are in a group of any kind and you are not creator, admin or mod, yes. They can take down anything they wish.
However, there may be other reasons.
Example, i have a really good friend of mine who posted in 2 of my groups yesterday. We follow all the FB
guidelines, but everything he posted was 'legit' and political, but it kept saying it was 'flagged' for removal
in my admin panel.
I had him post 'hi', with no pics, just hi. It got flagged too. It was associating his account with the flag as
someone reported them before for something they didnt like and he is 'under review'. Everything they post
now gets auto reported for a period of time.
I had to remove the posts, but didnt really like that i had to for FB to stop scanning the posts in group.
In short, did you ask the admin/creator why they removed your posts? And as their group? They can pretty much
do whatever they want with allowing or removing content.
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credited for the work done with clients. Or, reply to continue if further troubleshooting is necessary.