intermittent problem with submitting forms

I have four frontend forms on a website under development. Two will work, sometimes, two will not. I have confirmed it is not a caching problem. Nor a conficting plugin problem.

The error log isn't helping me. Maybe you can make sense of it:
Invalid argument supplied for foreach() wp-cron.php on line 111 and [wp_privacy_delete_old_export_files] => Array My understanding is that wp-cron typically sends errors when there are problems with the array. But I can't find any. I suspect you would need to look at the functions file, so maybe this goes to email. Thanks