Problematic and problematical are different forms of the same word. Both mean (1) posing a problem, (2) open to debate, and (3) unsettled. Though they’re both listed in most dictionaries, problematic is more common in 21st-century edited writing. Problematical isn’t incorrect—and, in fact, it was the preferred form before the late 20th century–but it is an unnecessary variant.
This ngram graphs the use of problematic and problematical in English-language books published from 1800 to 2000. It’s self-explanatory.