From what i see on the patch notes, stigmas and raider ranks will disappear, all your stigmas and ranks will turn into xp boosts at 5:1 ratio at a maximum of 40 xp boosts.
That mean you can earn all the boosts you can have if you are raider rank 8, have 8 stigmas accumulated, or a combination of both.
So, right now just buy some "lore" to rank up your raider rank to 8, or save 8 stigmas accumulated, and you will earn all the xp boosts you can have.
The update arrives on April 4.
That is what i understand from the new system and conversions, correct me if i am wrong
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On a side note, the connection problems can be fixed, even if there are no dedicated servers, maybe the update also comes with some bugfixes to the disconnections problem.