Add Frame Hold Bug.
If you have a clip that is 5 seconds long, and you "Add Frame Hold" at 4 seconds in, you cannot use motion keyframes/adjustments at any point after the '5 second' mark of the clip. So it retains the duration of the clip after the freeze frame (even though you can extend it to infinity), in this example, I can only make adjustments for 1 second after the cut, because that marks the end of the 5 second clip. This needs to be fixed so that I can freeze frame, then animate/adjust settings anywhere along the freeze frame clip.
I have the answer. I am u/jayce_likes_beans and I can fix it. All you have to do is nest the clip after extending it as far as you want, after you freeze frame.
John Pooley commented
I have replicated this issue and so has reddit user /u/Jayce_likes_beans https://www.reddit.com/r/premiere/comments/cxm9aq/help_whenever_i_add_a_freeze_frame_to_my_video/
This is item 512 in my Premiere problems spreadsheet.
One workaround would be to nest the clip at the same time as the frame hold. Nesting fixes a lot of issues!