Raid Finder shows Sigmascape V5 Savage as completed for the week

Date & Time: 06/FEB/2018 - 21:00 PST
Frequency: Unsure
World name: Hyperion
Character name: Sun Rise
Retainer name: -
NPC name: -
Monster name: -
Class/Level: WHM/70
Party or solo: -
In-game time: -
Area and coordinates: -
Housing: -
Steps:
1. Do Not Clear Sigmascape V5 Savage
2. Clear Sigmascape V6 Savage
3. Open Raid Finder and see that it shows the reward for Sigmascape V5 Savage as claimed

I would like to do Sigmascape V5 Savage this week and be able to participate in a 2-chest group please.

That's not a bug. It's normal.

You cleared O6S first.
If you go on an higher stage raid, a windows displays and warn you that if you queue and enter to that next raid but didn't cleared the previous one before, you'll loose every loots from that one and it'll be counted as "cleared".

I'm sorry to tell you that your O5S loot for this week are lost.

Like KDSilver said, when you enter in a higher-tier floor during periods where Savage has weekly restrictions, you forfeit all rights to loot (including Datalogs) from all floors beneath the higher floor. You don’t even have to clear the higher floor; just entering it is enought to forfeit the rewards.

You should always do the floors in order while there are lockouts present on Savage floors.

This is deeply frustrating as someone who is very new to the game, and very excited to participate in new content. I see no reason for the game to be structured this way. It's arbitrary and punitive.

I wont disagree with you... but the game did warn you this would happen.