I just encountered this same problem. The Greek text displays in the Source Language Tool, but not in the Parallel Passage Tool. Hebrew displays OK. Filters are set to show “All Parallels”, and “Hebrew/Greek Text”. Starting Paratext while holding down Shift had no effect.
Paratext 8 was installed for the first time 2 days ago.
Windows 10, French UI. Paratext in English UI.
I reported the problem in Paratext.