Par for the course with my London experiences the past few months. The pre-upgrades still happen, but not until early on the morning of arrival.
Having spoken to staff at the Hilton Euston and Hilton Bankside, both mentioned that they moved to this to allow for late bookings to still get an upgrade, as well as to disincentivise people booking multiple hotels and waiting for the best upgrade before the cancellation deadline. Bankside will still upgrade the day prior, but it depends on occupancy and they are finding it is more on the day now.
Of my last 15 stays in the past few months, only the DT London West End has upgraded consistently the day prior. Every other hotel has been on the morning of arrival.