Dragging photos from Apple Photos library to an album only adds some of the selected photos

Dragging photos from Apple Photos library to an album only adds some of the selected photos

I have an Apple Photos album with 382 Instants in it. I would like to add all of these to a Peakto album.

I begin by selecting all 382 photos with ⌘A. I then click one of the selected photos with the mouse and start dragging it.

A little red bubble pops up by the cursor, which is supposed to show the number of selected photos. However, it shows a seemingly random number between 39 and 104.

If I drag the photos to the Peakto album, it only adds some of the photos, not all those I selected. It seems like the drag operation does not pick up on all the photos I have selected.

I have a screen recording but would prefer to share it with the Peakto team privately.

I really want to lean into Peakto, but this sort of thing does not inspire confidence :(