I just ran into this issue today as well. Anytime I create a new railing, if the renovation filter for Existing Elements is set to "Hide", my rail will not display, regardless of MVO settings or line types/fills. The "Show on all relevant filters" button referenced in the thread mentioned above does not work for me, and all the sub elements of the railing show "New" under the renovation status.
What did work for me was to set the renovation filter for Existing Elements to "Show", then set the railing to the Existing renovation filter, then set it back to new. Then I can switch the Existing Elements renovation filter back to off and it continues to show in my floor plan.
This "bug" happens whether it's a new railing or if I eyedrop it from an already "fixed" railing. (One that I have set to Existing then back to New in order to display correctly).
AC 24 US
Windows 10, AMD Ryzen 7 3700X, 16.0 GB Ram, AMD Radeon RX 5700 XT