If Swahili is a phonetic language, why are misspellings common?

Right so according to research, misspellings such as th instead of dh, r instead of l, the omission of h, etc. as can be seen here:
https://www.researchgate.net/publication/242189390_Problems_of_Writing_in_Kiswahili_A_Case_Study_of_Kigurunyembe_and_Morogoro_Secondary_Schools_in_Tanzania/fulltext/0285f12d0cf2effb422c6b26/Problems-of-Writing-in-Kiswahili-A-Case-Study-of-Kigurunyembe-and-Morogoro-Secondary-Schools-in-Tanzania.pdf?origin=publication_detail
Every language has its irregularities but Swahili is phonetic so misspellings shouldn’t be common. Is Swahili really a phonetic language overall but has a few irregularities or are resources just gaslighting people that it is phonetic and in reality, Swahili isn’t? I’m feeling suspicious

What do you mean by phonetic language. Every language has phonetics.

Phonetically consistent

That doesn’t seem to mean anything. All languages have phonetics.

Presumably the OP means that Swahili orthography is highly phonemic, not that the language is.

But I wonder if the OP read the article that they linked to, since it explains some of the reasons for spelling errors produced by Swahili students.

Some ethnic community languages in Tanzania do not have the sound [ð] in their phonological systems (Massamba 1986). Such people use the spelling /th/ pronounced [θ] instead of the standard Kiswahili spelling /dh/ and pronounced [ð].

The coastal ethnic groups near Dar es Salaam city, like the Zaramo and the Ndengereko, drop the phonemic /h/ where standard Kiswahili word begins with the letter /h/. The Kurya ethnic group in Mara region does not have the sound [I] in its phonological systems (Massamba 1986). As a result, speakers use the phonemic /r/ in place where standard Kiswahili uses /l/. It appears, therefore that, the wrongly spelled words cited in (a), (b) and (c) above are a result of influence from ethnic mother tongues.

Ok I understand dh, and h problem but the article states:
" The Kurya ethnic group in Mara region does not have the sound [I]

in its phonological systems (Massamba 1986).". In the article, the l looks more like an uppercase “i” to me.

I am Finnish. We have about 95% phonetic spelling. There are still words that are pronounced a few ways. Also, there are sounds that are hard to produce with letters. The ng sound is one sound. It and the similar nk are in use. It appears in shoe: kenkä, kengät (plural). So it is quite possible to spell things very close to how we pronounce. But it is mainly due to limited sounds i Finnish. We have no sh, ch or w, though we pronounce foreign words with w as ui. The main reason for the phonetic spelling is the late arrival of printed Finnish. Nearly everything was printed in Swedish till late 1800s.

Like?
One more thing: In Finnish, present tense indicates both present and future

Well, more like dialect or spoken Finnish. If you are not well schooled, you make these mistakes where the spoken is just slightly different. Enään for enää (anymore). People are often confused by the -n ending, such as tänään (today) and try to stick it elesewhere too. So the people are just spelling a common word wrong, not “proper Finnish.” Tekee is to do, some dialects use tekkee. People say humenna for huomenna, tomorrow. If a Finn read the words off a page, there would not be too much wrong, except borrowed and educated words.

One other type of misspelling or pronunciation in Finnish is with foreign names. For example Caucasus is Kaukasia. People pronounce it Kukaasia. Finns use a lot of double vowels. Aasia is the Finnish for Asia.

Actually, the double consonants are at times the same. People pronounce kuulostaa (to sound like) as kuullostaa, and some misspell it that way. It’s derived from kuulla, to hear.

Finnish is indeed a complex language. So in summary, what appears phonetic about Finnish is unphonetic to the foreigners

Well, mainly to English speakers. Most of the letters are pronounced as in Swedish, for example. What Finnish has that is unpronounceable is diphthongs: au, ua, oi, io, yö, öy, äi, iä. The umlauts are the same as in Swedish.

You mean, they are “hard to pronounce”?

Well, they are not hard at all. It is just the Americans cannot pronounce them. The common ones like “house” they can.

Swedes pronounce them way better