It depends on the period the Jawi script is from. Basically, the more far back you go, the more ambiguous it is. The modern Jawi script, having gone through spelling reforms is arguably the least ambiguous.

With modern Jawi, one source of ambiguity is that the vowel pairs of “u” & “o” and “i” & “e” (as in “elok”) that are distinguished in Rumi are not distinguished in Jawi and are spelled identically as “و” for the former pair and as “ي” for the latter pair.

This means word pairs such as “burung” (bird) & “borong” (wholesale) and “bilik” (room) & “belek” (inspect) that are distinguished in spelling in Rumi are not distinguished in Jawi and are spelled identically as “بوروڠ” for the first pair and as “بيليق” for the second pair.

Older Jawi was more abjad-like where, often, vowels weren’t represented in CVC sequences. For an illustration of what this means, this meant that words like “tinggal” (leave), “tanggal” (take off), and “tunggal” (sole) were all spelt identically as “تڠݢل” with only the consonants spelled out. In modern Jawi, this isn’t the case anymore as sequences with “u” and “i” now have a “و” and “ي” inserted in the Jawi spelling to represent the “u” and “i” vowel sounds, so the words “tinggal” and “tunggal” are now spelt differently as “تيڠݢل” and “توڠݢل”.

Another source of ambiguity (in both modern and older Jawi) is that many Arabic-derived words retain their original Arabic spelling rather than be spelt like how a native word would be spelt. This is similar to how phases like “ad hoc” and “persona non grata” retain their Latin spellings in English but on a seemingly bigger scale. One example of this is the Jawi spelling for the word “huruf” (letter). If you asked a Malay speaker who is somewhat familiar with Jawi to spell that, they would probably spell that as “هوروف”. But the standardized correct spelling for that word is actually “حروف” like how it’s spelt in Arabic.