Oh hey im so sorry for the late answer, i managed to kind of work around it by copy -> paste -> "Zero Angle"-Button -> manually re-aligning if there was an angle i wanted to preserve.

I tested with a minimal setup:
Test scene.c4d

If you copy ease from the 2nd Y keyframe onto the 2nd X keyframe, the break shows in cinema version 2025.3.1
I think this only happens if the keyframe from which you copy has broken tangents and an angle. It seems it also kind of breaks the "Keep Visual Angle" function (at least often) into not functioning anymore for that keyframe.

Anyway thank you so much for taking time for this out of your vacation. There is no urgency anymore so feel free to close this or check it out after vacation

All the best

Hi Dr. Sassi im behind in a project and need a fast fix for my problem.

I guess its a bug or limitation. I hope there is a fix or workaround.

If i copy the ease of one keyframe and paste it back to that exact keyframe or any other keyframe, that ease is not the same anymore because its tangents are not keeping the same visual angle anymore. Not sure if this only happens with keyrames that only have broken tangents (i need to break them to make them longer on one side but i keep visual angle doing it).

I select this keyframe and copy the easing:

This is it after pasting the ease:

If i paste it to different keyframes, they just break into uselessness:

They all break differently but they all break:

Questions that come to mind:
Is there a way to copy+paste interpolations of broken tangent keyframes and maintain the visual angle?
Is there a way to restore visual angle like the "Zero Angle (tangent)"-Button does but without actually zeroing out.. just re-aligning the left tangent to fit the right one?
Is there a way to elongate one tangent (but not the other) without breaking tangents?
Any other way this problem could be fixed?

Sadly i cant just redo stuff fundamentally because i cant redo the whole animation. Its due today