I already have that bug, where my prestige evel has dropped, but only restart the game and it was correct again.
But by the video i think you are incorrect in some interpretations.
We have 3 "diferent levels".
1 - prestige level (the one wich really dropped)
2 - rank level
3 - seasonal level.
Your seasonal is "righT.
About your rank level, i see you "circling" the hightest rank you reached (in your case was 5) but now its 7. That happens because every seasonal start you drop 2-3 ranks, so ii your hightest level was 5 and we are at the start of a new seasonal, i think your rank in 7 its correct
I had the same issue several times - suddenly my Prestige dropped to 1 and I could access the seasonal mode or unlock rewards from the seasonal trees. A restart always fixed it for me. Usually, it happens at the beginning of each season.
Prestige level acting funny is quite common. For me it sometimes just shows lvl 45 Prestige 0 (tattered border). But It seems this issuue is with the player's rank and play modes becoming locked out.
Definitely deserves a support ticket.