All completed issues and epics disappear from my plan once statusCategory is done.
As far as I could understand, Advanced Roadmap seems to be using statusCategory to determine if an issue is "DONE".
I've tried setting the "keep issues in plan days" field to 999 so I can keep the issues visible, still they are not shown.
It was mentioned in another thread that all issues should have resolutions date set. Not necessarily issues in a statusCategory Done have their Resolution set in JIRA. Only if you choose to do so via postFunction on Transition to the status.
So if you are relying on Resolved field in JIRA (for the Resolution date), why don't you rely on Resolution field not being empty to choose which issues are "Completed" for the purpose of your filter?
JIRA doesn't impose this on its users, it is a shame that if we want to use Advanced Roadmaps we are forced to revamp Workflows impacting thousand of JIRA issues and metrics.