I in fact see all the episodes listed in the Episode list, I must have done them the first 1-2 weeks after Gamma Expansion. I don't think I've tried doing them since, but I've confirmed they are not loaded in my Journal, and yet REPLAY is completely missing.
As a result not a single Gamma Mission can be done again. This is NOT the case however my my 2nd Character a Gem Hadar (Gamma Recruit) who does in FACT see REPLAY in every Gamma ARC options. Is this normal?
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UPDATE: [FOUND CAUSE] - Somehow Renegade's Regret which I likely (I'm pretty sure did when Gamma Season opened had SKIP beside it. It was also in the Journal but I'm pretty sure I was doing it over again for the secondary trait or intended to. Yet immediately upon selecting SKIP then all Gamma Missions became available and were instantly updated to REPLAY.
So a little unusual but just a bit of 'slight' confusion.