oh gosh that's really troubling! other people seem to have lost their save data after the game updated too for some reason, even though itch SHOULD be keeping it ;-; (and does keep it 90% of the time)
but if playing the windows version (the downloaded one) is an option to you, I can give you one of my save files on whatever point in the game you stopped! also, chapter 6 is already in development, so it should be out either by the end of this month or the beginning of february xD