This has been happening for some time over at least the last few releases. When choosing "Library" from the main toolbar, the CPU immediately spikes to 100% and stays there until the pane is closed or the app is force-quit. There is an article that mentions it could be related to indexing but the app was just upgraded to v49.0, performed the indexing, and the indexing completed. This still happens every time the library pane is opened and resolved when the library pane is closed. This essentially makes the Library pane unusable.
Dragging the library icon from the toolbar into a tab area makes the library usable so I'm using this as a workaround.
Has anyone else seen this behavior?