Refinablestrings in SharePoint search webparts do not come through

[jvrc98]

Reporting an Issue

We want to add two lists together in one SharePoint search using the pnp components (this works).
So each item from a list is one item in the search. (So if list A has 50 items and list B 60, we have 110 items in the search.)

Expected behavior

These two lists have columns that are named differently, but the goal is to add one column (f.ex. 'Archivetheme') from list A and one column (f.ex. 'Theme') from list B under one column in the search by using a refinablestring that contains both columns.
The first item is one from list A, so only column 'Archivetheme' has a value and shows the output (column 'Theme' value is null).
If the item is from list B, the column 'Theme' has a value, but column 'Archivetheme' from list A not.

Actual behavior

But the result for the refinablestring in the search results is 'null':
search refinablestring:

debug output search results pnp component:

Anyone who knows the solution to this problem?
It seems that our refinablestrings always give 'null' as a result (also with this Title ref.string: Basic:#10, ows_Title, Title).
I would like to use this refinablestring in the filter webpart eventually.

What we already tried

• to add the values to new refinablestrings
• created a new page
  --> but the refinablestring still gives no value/output (just 'null')