So I noticed in the TWAB that the season pass is flashing for some players, this is the case for me but i think I know why. In game my whole season pass is collected, however when I check my status of the season pass on bungie.net my Level 92 reward (Twisted Energy) is sitting unclaimed? Maybe this could be causing the issue? This shows as available on my Hunter and Warlock but NOT my Titan on bungie.net, all collected on the season pass in game. I hope this helps!
Bungie can't code so it's hit or miss. It happens to me but not my cousin.
Also yea it flashes when you have unclaimed rewards. However some of us claimed them all and it still flashes.