“Retention bonuses” are a known fact and on the UK based HfP website forum there is a dedicated thread to this for Platinum. It is a bit Random but there are system flags apparently that drives how much they can offer. Per page because I have a long history of continue account on my BAPP and get a retention offer every year when calling about considering cancelling (a promo applied to the account in reality, 10,000 Avios when spending £3k in 3 months), but I only ever got offered 35,000 MR on my more recent Platinum account. For me they have also been clear that it is only once a year (if I call before 12 months have elapsed from my last offer, they tell me there is no retention offer on my profile and call after xx date) but there are reports on HfP of people getting multiple retention offers per year.