Re-subscribe to a plan after upgraded to other

Hello,
I can't seem to be able to resolve this issue of a plan no longer being available for a user after they "upgraded to other" 
In my setup I have 3 plans: monthly, semiannual and annual. They are all "registered" but they pay accordingly, i.e. monthly, semiannually or annually. Some users upgrade from monthly to annual, and then want to go back to monthly after they've "upgraded".
The problem is that, even after expiration of all plans, the monthly plan is still not available. 
All 3 plans are exclusive and are set as "No: It will be possible to upgrade to this plan (for free with pro-rating) if all conditions below and elsewhere are met".
As Kyle described in this thread:  www.joomlapolis.com/forum/developer-members-support/244079-subscribe-to-one-plan-unsubscribe-from-another-plan#325490
The proration is working fine, and they don't mind waiting for the upgraded subscription to expire before going back to the monthly subscription, but the issue is that it does not show at all, even after all plans are well expired. 
Right now, if someone wants to go back to the monthly subscription, I have to go to the old subscription and switch it from "Upgraded to other" to "expired" and then they can sign up again. 
Is there anything that I'm missing? 
Thank you,
Tomás 

Normally you should be able to revert to the older plan after expiration or cancellation, but there might be some cases where this isn't allowed such as upgrade permissions. Ensure all your plans always allow upgrades with the below settings and that should ideally work.

Price
Can be reactivated if expired or cancelled since more than: Can be reactivated anytime
Can be reactivated if expired or cancelled since less than: Can be reactivated anytime

Workflows
Allow upgrade to this: Yes
Propose plan for upgrades only if it is more expensive: No: It will be possible to upgrade to this plan (for free with pro-rating) if all conditions below and elsewhere are met
Propose spontaneously plan for upgrades: Yes: show automatically plan for normal upgrades (recommended)

I however recommend for your 3 plan setup maybe considering replacing it with CBSubs Options. With CBSubs Options you can have 1 plan with 3 different pricing options. Example of this feature can be found in my blow below.

www.joomlapolis.com/blog/kyle/18983-cbsubs-options

Hi Kyle,
Yes, those are the settings I have on all 3 plans, but it still won't allow to re-subscribe to the original plan. 

I was not aware of the CB Options. I will definitively look into it. I have several hundred subscribers, so I would have to create the new plan and then not allow new subscriptions to the old 3 so that users will slowly migrate to the the new options plan? Or could I add the options to the existing plans?  
Thanks
Tomás

Do you have any conditions configured under Workflows or any limitations applied by ACL under Access?

Or could I add the options to the existing plans?  

You can enable it on an existing plan. They can then change their pricing option on next renewal. If auto recurring they'll need to cancel to change their pricing option before next renewal though.

Hi Kyle,
I have no limitations on the monthly (original) plan, which fails to show as an option to downgrade and all plans are publicly available.

The year and semiannual plans have the restriction that a previous plan (monthly, semi or annual) must be in state Active, Expired, Unsubscribed or Updated to other. The reason for this is to have new members sign up for the monthly plan first, and only after they've been approved and have been members they can pay to an annual or semi annual plan. 

I will test the CBSubs Options and my goal would be to have one plan with the different options, probably the monthly plan as it's the most popular plan, and then phase out the other two, though if it's not displaying for upgraded ones it can be a problem. 

What would be the best way to "phase out" those plans, meaning allowing them to continue as they are, on recurring payments, but no longer showing as an option to renew, so any renewal would be forced to the Options plan? 
Thanks,
Tomás 

Believe this maybe working as intended since the upgrade process is a forward process. There isn't a downgrade process which would cause a lot of strangeness when it comes to allowing prorating. The best I can suggest is reverting their old plan from an upgraded status to an expired or cancelled status, which you could automate using CB Auto Actions. This however as noted could cause weird situations of them downgrading in the middle of their subscription causing their downgrade to be free due to prorating.

Typically the best way to allow for forward and backwards plans is to have all 3 as non-exclusive then use conditions to limit access. So for example they can't upgrade to a new plan until their current is cancelled or expired. This would allow them to then select a different plan. All of this is really the old way of dealing with this though and CBSubs Options is what everyone should use if they need multiple pricing options for a plan.

What would be the best way to "phase out" those plans, meaning allowing them to continue as they are, on recurring payments, but no longer showing as an option to renew, so any renewal would be forced to the Options plan? 

Configure them to no longer accept new subscriptions. Then just let them continue to function until nobody is on that plan anymore.