For the current version 26.2.26 I can confirm that exporting a video with a ‘keyframed’ Reframe filter from the timeline works well, as it was treated here: Reframe filter does not export keyframes in V 24.10.29 - Bug.
The presumably unsolved part of the issue is, when exporting from a timespan marker, the keyframes are (still) unregarded.
Setting the advanced option progressive=1 does not make a difference, with reference to Export in advanced mode with reframe and keyframe.
Export from a timespan marker is a useful feature though. Please consider a possible fix.