It does go back, I can confirm. But if you get to the end of the bar when it’s in the 50,000 Alpha state, it might reset to 0 even when you resubscribe (didn’t have to test that yet, thankfully). It appears to keep track of your percentage of the bar’s completion, and not the hard amount of SP that you’ve accumulated.
My personal opinion. the whole bar sp system is stupid.
I have different stands on several characters. after fulfilling a bar the system jumps to a new one without crediting what was collected. Just confusing stuff.
As I have written here and still have no answer I do not even see alpha rewards.
Bug over bug in this game, and that after so many years