The bug is an old and general one when you do not specifically drag clips from a file manager to the timeline in a new session. For example, start Shotcut, open an existing project and try it: occurs on every old version. Playlist + is not a clipboard paste but rather appends what is in the Source player. Now, Copy does both add to the clipboard and Source player, but the Playlist + is sometimes not observing that there is something in Source until you switch to it. In your example, it is something subtle that changed with the UI/actions revamp in this version. Low priority but thanks for reporting it.
I’m new to Shotcut and encountered this same issue. I may have a workaround for anyone else viewing this thread. I couldn’t drag my media file from my Files directly to the Timeline (the application crashed). This is with Shotcut v22.12.21 running on Fedora 37 Linux. I can however drag a media file from my files app to the Source Player or open it via the menu. Then click and drag from the source player to the timeline. And as noted in the previous post, clips cannot be added to the Playlist. My workaround is this: simply reopen the media file from the menu. Now clips can be added to the Playlist.