Please can you provide more information with what the issue is? The forms aren't displaying? not processing? not emailing? not mapping to the placeholders etc etc? When did the problem occur? How many sites has this effected? Are they all on the same provider? What version of MODX etc.
Did the hosting provider update the version of PHP running on the server?
If they did can you experimentally return to the version that was previously running and see if if resolves the problem?
https://forums.modx.com/thread/101969/modx-revo-formit-php-7-1-problem
discuss.answer
Thanks for your help everyone, but I think I have cracked it.
It seems that either the new version of cPanel or FormIt was more strict when it comes to the having a specified emailFrom. So previously the form would have sent without it set, but in the new version you had to have a valid emailFrom set for the email to go through.
It's simple enough to fix, and makes sense that you would need it. So all's good now.
Thanks again