Just tried to a video transition to a Multicam timeline between a camera switch and it does add the transition in the timeline but only plays back as a cut as if no transition was applied. Also, using the shortcut CTRL D doesn't add the transition but does it show up in the history that it applied a transition.
I used a Dissolve transition and it shows the video dissolving between the 2 video source in the transition Effects Control window, just doesn't work in the timeline when playing it back. Rendering the timeline doesn't work either, still a cut transition.
Actually, just tried the CTRL D shortcut and it is now working.
Now the transition shows up when going to the Export menu and looking at the video in the Preview window and when exported the dissolve is there so the only problem is that the video transitions can't be seen when playing from the timeline.
Decided to close down Premiere, restart it and reload the project and now the transition works in the timeline.
Actually, here what happens. You can't see transitions when the Program monitor is in Multicam mode, you need to switch is back to Composite mode then the transition will preview when playing from the timeline. Now I just checked and you can scrub through the transition and see it when the Program monitor is in the Multicam mode.