It seems like there's a bit of inconsistency for what is considered a "displacement"
Most abilities that "move you" are categorized as a displacement currently. This is stuff like Bebop Hook, Abrams charge, stuff like that.
But also abilities that knock you up, lash 1, bepop 1, Holiday 1, billy 1, are also categorized as displacement.
It seems like knock ups do not actually trigger reactive barrier, but displacements do, it's quite likely that, in the patch notes, the first version of displacement was the referred one, so stuff like hooks and Para ult.
By testing in sandbox you can see these still work.
As for knock ups, nothing has changed, here's how reactive barrier triggered in the December 2024 version:
View attachment 2025-09-30 15-04-07.mp4
All that being said, this
could still be a bug, but it's been there for a long time and it's only specfically for knock-ups (again, Lash Slam, Holiday Barrels, Billy's Bash, Bepop's Uppercut)