Since 1.11 lava flows slower in the end dimension at a rate of 30 ticks. In previous versions it was flowing every 10 ticks like in the nether. According to MC-7457 the faster flowing speed of lava in the nether and end dimension was intentional.
Linked issues
Comments 5
Probably caused by the change in 1.11 that made maps work in the end (and split off some of the properties of the nether and the end, such as presence of skylight).
Can confirm for MC 1.12.1.