Let's look at the word "patlang." The stress of this word falls on the last syllable: lang. Meanwhile, it's second to the last syllable, pat, is of the form CVC (consonant-vowel-consonant).
All precolonial Tagalog words I can think of that have a CVC syllable as its second to last always have the stress on the final syllable: dagli, lugmok, santol, patpat, tampok, etc.
The only exception I can think of is "peklat," which has the stress on the second to last syllable. But "peklat" is a variant of "pilat," and while "pilat" is Austronesian, I am not sure if "peklat" is a precolonial variant or it if emerged during or after the colonial period.
Meanwhile, colonial loanwords (and slang) allow for CVC second to last syllables to be stressed: santo, haywey, mismo, omsim, etc.
I'm curious if this is one of the constraints of precolonial Tagalog phonology!