Actually, “rama” (branch), “cama” (bed), “mucama” (maid) are all femenine.

“Centurión” (roman military rank) and “esturión” (fish) are masculine

Correct. "tema", "teorema" are masculine because they are cultisms, derived directly from greek. Same with "fantasma" and "miasma".

bad 'reason': problema is greek too ⲡⲣⲟⲃⲗⲏⲙⲁ 🇬🇷 problem

And it's masculine too in Spanish. Isn't it in Greek?