As per InsideFlyer:

https://insideflyer.nl/flying-blue-b...icatieperiode/

Source is unclear, but it is claimed that anyone having a positive rollover in 2019-2020 will keep/get a minimum of that same rollover for 2020-2021 due to not being able to fly during Covid times. If true it sounds like FB has heard the (many) people complaining that they 'lost' their buffer of XP's that was collected/saved (including myself).

Edit: Official now: https://pages.flyingblue-info.com/FB...tml/#surplusXP