Plan not showing on Sign up page

Kyle - 
I have a number of exclusive subscription plans.  The most popular plan stopped showing up in the selection list.
this plan hasn't changed in years.
I've reviewed all settings, and tried all normal tricks, but it won't display.
I set it as "Selected by default" to force it, but the plan shows for only an instant, then disappears.

I'm out of troubleshooting options.
Any ideas?
Fred

Edit your plan then check the following settings.

Workflows
Allow registration: Yes
Propose spontaneously plan at registration: Yes: show automatically plan for normal registrations (recommended)
Conditions: (if you've any conditions here please be sure they're configured properly)
Access
Published: Yes
Allow new subscriptions: Yes
Allow access from site frontend: Yes: this plan is visible on the site (recommended)
Visible for Access Level: Public
Visible for Group (and above this group): Public

That should be all you need to ensure visibility on registration.

All the settings are confirmed...
I've also reviewed all the other plans to ensure someone didn't mangle a condition.  

Workflows
Confirmed - Allow registration: Yes
Confirmed -  Propose spontaneously plan at registration: Yes: show automatically plan for normal registrations (recommended)
Confirmed -  Conditions: (if you've any conditions here please be sure they're configured properly)
   All Exclusive plans (except this one) are selected in "None of the following plans can also be selected"
Access
Confirmed - Published: Yes
Confirmed - Allow new subscriptions: Yes
Confirmed - Allow access from site frontend: Yes: this plan is visible on the site (recommended)
Confirmed - Visible for Access Level: Public
Confirmed - Visible for Group (and above this group): Public

Still scratching my head over it...
Fred

Try removing the condition and see if that resolves your issue. If it does not please PM backend super user login credentials and include the name of the plan giving your troubles and will take a look.

I've solved it...  
Someone has added an extra "required field at registration" inside Dynamic Conditions that isn't prepopulated - it was hidden among the others, so I missed it.
Close the ticket.
Thanks,
Fred