It used to save the linked cel array which contained the canvas nodes into the .pxo. This, however, does not make sense, because the canvas nodes are being recreated when a .pxo is loaded. Therefore, they are different nodes than they used to be.
Now, an array containing the frame numbers which have cels linked for each frame is being saved and loaded into the pxo.
Pixelorama now requires at least Godot 3.1.2 or 3.2.x to work, because TranslationServer.get_loaded_locales() was not included in older versions. If you're using an older version of Godot, please update. Godot 3.2.1 is the currently recommended version, until 3.2.2 is out.
Also updated the list of the translators.