Platform, device version and operating system
What you were expecting to happen, and what actually happened
If you win the guild wars on sunday, you get a double XP bonus for Monday. I expect it to expire on Tuesday, but it lasts until the next guild war starts, two weeks later.
How often does this happen? When did it begin happening?
Every time you win GW on sunday
Steps to make it happen again
Win GW on Sunday. Retrieve your mail on Monday with the 50 extra guild seals and the 100% XP Bonus. Wait until Tuesday and check your bonuses. +100% XP for special events is still listed