I've only heard it sta-sis with short a like in cat
According to Wiktionary is can be stay-sis or sta-sis
https://en.m.wiktionary.org/wiki/stasis
I thought
Stasys was stah-sis (long a like father) when I first saw it but that is because my brain knows y as short i because it is short i in Ukrainian transcription, Russian transcription, Belarusian Latin, Polish but in Lithuania they say it kind of like stuh-syees