The “main” version is built on Ubuntu. There is a Debian based version (LMDE), but the Ubuntu based one is the “recommended” one.

If you can, try deleting all the partitions and re-create them using GPT instead of DOS (MBR) and see if it then shows the same. Also agree that you should make your boot partition 1G.

I just looked up the initial release, it was in August 2001. I don’t remember the first time I used it, but it was probably 20 years ago. Still remains my favourite for the reasons you mentioned.