This may be way off base, but when you logged in to your main - did you have a note about it being eligible for a gear update?
And on your character selection screen, do you happen to have this icon available?
I’m just curious if the “boost” being processed wasn’t the new gear update system, since it carries a lot of parallels with the regular character boosts. If you have that W icon showing on your selection screen, that means you’ve still got your expansion’s free level boost available to be used.