I think you’ll just need to troubleshoot each sub-expression independently to find where the breakdown is. I would suspect that one or more of the three LOOKUP() expressions is returning a blank value, which then causes a cascading failure.
To test, I’d go to the same table that has the current expression, add a new virtual column, edit its App formula expression, then use the Test feature of Expression Builder to try each sub-expression and confirm you get the results you expect. After testing is complete, you can delete the virtual column.