The M25 J5-J8 are having Speed Limit Tests applied. These seem to be highly irrational.
You start with a speed limit test, followed by another nonsense message such as congestion ahead or report of object in the road. These make no sense.

Apparently these tests need to be carried out when there are no roadworks. There are no roadworks this weekend because it is a bank holiday and they were removed to speed up traffic flow. Motorways work best when everyone is doing the same speed. Adding pointless 50mph sections encourages some drivers to ignore it leading to a 2 speed motorway which is clearly dangerous.

These tests have been going on for months. They are either poorly designed or ineffective.