Tutanota icon issue
After a recent update of the Tutanota app (de.tutao.tutanota), to version 1.9.4, the TwelF icon disappeared and the app reverted back to its default icon.
Side note: before this update, when your icon was working, the app would throw an error when it tried to generate a notification. I recall another application doing this, so I thought I would inquire about it here.