Have reviewed your install and believe I understand the issue. The test user provided upgrade path appears to be as follows.
Outdoor > Minimalist > Freedom > Parking
These are all upgrades from 1 plan to another. Now as subscribed to Parking you want to allow them to upgrade back to say Minimalist. When doing this the Minimalist plan is not displaying on its plans page or in the profile tab.
This is due to "Propose spontaneously plan for upgrades" being set to "No: hide this plan from upgrades and from access proposals, unless specifically included in URL". You need to set it to "No: hide this plan from upgrades, unless included in URL or needed for access", which appears to resolve your issues in my tests. Currently you're strictly only allowing the plan to be accessible if it's an upgrade, which Minimalist isn't since you already upgrade to and from it.