Fix nested family parameters that “disassociate” in Revit

TL;DR: Nested parameters “break” when the host and child aren’t set up to talk the same way. Match parameter types, associate the child param to a host param, and make the nested family Shared (when you need to tag/schedule it). Test swaps only between nested families that expose the same parameters.

Why it happens

• Type mismatch. Revit only lets you associate parameters when they’re the same data type (e.g., Length↔Length, Text↔Text). Otherwise the link won’t hold. 
• Not actually associated. To drive a nested family’s parameter from the host, you must Associate Family Parameter in the host (the “link” step).
• Shared vs not shared. If you need the nested component to be selectable/taggable/schedulable in the project, it must be Shared; otherwise it won’t appear as its own schedulable item.
• Swapping inconsistencies. When you swap one nested family/type for another, the new one must expose the same parameters (same names/types) or the association can break.

Do this (fast)

1. Standardize parameters.
   Define needed parameters in your nested families with the correct data type; use Shared Parameters only when you need to tag/schedule across families.
2. Share what must be scheduled.
   Set the nested family to Shared if you want it to appear in schedules/tags as its own item.
3. Associate in the host.
   In the host family, select the nested component and Associate the child parameter to a host parameter (that you create if needed). This is the supported workflow. 
4. Plan for swaps.
   If you’ll let users swap nested types, ensure all candidate nested families expose identical parameter definitions so the association survives the change. 
5. Reload cleanly.
   After edits, reload the nested into the host, then the host into the project to propagate changes.

FAQ (quick hits)

• Can I drive nested instance parameters from the project?
  Yes—by associating them to host parameters, which you then modify in the project.
• Do parameter types have to match?
  Yes. Length↔Length, Yes/No↔Yes/No, etc.
• When do I need Shared Parameters?
  Use Shared Parameters when you need to tag or schedule values across families/projects; family-only values can remain family parameters.

Bottom line

Keep parameter types aligned, associate child→host, share components you must schedule, and standardize parameter sets across swappable nested families to prevent “disassociation.”

Sources & further reading

• Revit Help — Use Nested and Shared Families (behavior, when to share) 
• Revit Help — Associate Family Parameter to a Nested Family (how to link) 
• Autodesk Support — Map nested family parameter to host (step-by-step) 
• Revit Help — Create a Nested Family with Interchangeable Components (designing for swaps)
• Revit Help — Parameters / Shared Parameters (when/why to use)