I have two cat palms and one of them turned black at all of the stems/base/trunk and nearly died. Now my second one has the same thing happening in a localized spot. I bought these from 8 months ago.

facts: I haven't changed the potting soil, I water them once a week, I
live in Florida and the plants are kept indoors not in direct sunlight,
On the first cat palm the black stems slowly spread throughout before
the whole thing went brown.

Help! How can I avoid this?!