Panels that have been previously marked for review, whether or not they have been subsequently noted, will NOT appear with the notes/marked for review indicator until you select them.
This was caused by some erroneous code in the Flix UI.
The best workaround found for this is to select the first panel when a new sequence is loaded, then press and hold the right arrow key. This will 'select' each panel, which will trigger the orange marked for review indicator, and notes to appear. You may have to go over the sequence with the arrow key more than once, as Flix traverses the sequence very quickly, and some panels may be skipped on the first pass.