Reading toki pona is far more difficult than writing it. Valid toki pona can be read many ways and has garden paths (places where you need to back-track and re-think what you read). So as you read along, you need to have this sense of the odds that a phrase is parsed one way or the other that mostly comes from experience.
Invalid toki pona even harder to read because you have to parse it with common errors in mind. It boggles the mind that to read toki pona, you must have in mind a correct grammar and several alternate defective grammars, parse a sentence using all of them and then someone pick out which one was meant.
Still, there is a class of errors that are effortless to read. I think that the reading gotchas and the effort-less to read mistakes are signs of mistakes or limitations in the conlang’s fundamental design– underspecification and overspecification respectively. The grammatical errors that are likely to completely throw the reader off track are errors of the writer and not the language.
Parsing gotchas- Reading Valid Toki Pona
That first sentence might be a conditional.
The last word could be a modifier or someone/something that owns it.
The ni could refer forward or backwards and can refer to sentences, things, and things in the environment.
The ona could refer forwards or backwards and can refer to things and things in the environment.
post-verb, pre-e words can be a noun complement or an adverb.
The participle-like word might be first or last. Sometimes these have a verb/adverb reading as well.
waso tawa. running bird.
tawa pona. good running.
pana mani. monetary giving (payment)
The "x li lon y e z" construction feels backwards because place normally comes last (or at least late in the sentence).
The "noun li noun e noun" construction will probably be read with the noun as a verb 1st.
jan li pali e musi. The man turned the game into work. vs The man enganged in a game.
Predicate vs Intransitive readings
sina suli. You're fat. You are growing.
Modifiers to mi and sina (rare)
sina suli li tawa. You're fat/growing and are walking, vs You, sir, are going.
Some polysemy borders on homophony (most meanings are similar, some are getting kind of different)
pona means wash.
sona means understand.
Some meanings border on contronyms
awen - to keep doing something
awen - to hold, as in to stop.
physically near vs collaborate
Mind reading anaphora. You know what ona and ni refer to, I don't.
Short noun phrases. I read it with one of the basic meanings, you mean one of the obscure meanings.
mi, sina, ona mean us, y'all, and them, too.
Parsing invalid toki pona
These errors can be very difficult for the *reader* to recover from
A particle may have been dropped. pi's and e's most likely. Missing li is problematic for sentencesd with complex subjects.
An e phrase may have been dropped. Usually not problematic.
A 2nd li phrase uses the object of the last sentence as subject.
* mije li lukin e meli li tawa lon esun.
Means A man saw a girl and he was walking in the store.
Not "A man saw a girl walking in the store"
Minimal pair confusion. If a sentence doesn't make sense, try mentally swapping out the minimal pairs with its alter-ego.
a/i/e confusion is really bad for readability
missing period. In general, where phrase splits aren't explicit, reading is harder.
Some errors are (mostly) effortless to recover from *for the reader*:
period instead of colon after ni
extra li for mi/sina
missing noun for a proper modifier
lower case proper modifiers.
missing "e" sometimes, because adverbs are rare and you can parse the DO by position.
dropping lon from a prepositional phrase, e.g.
laso suli li lon sewi lawa mi
laso suli li sewi lawa mi.
pi missing before mi mute/sina mute. No one shuffles modifiers and mi mute/sina mute.
n/m confusion is a non issue.
ala could negate the previous single word, or the entire phrase.
mi wile lukin ala e sitelen tawa.
mi wile ala lukin e sitelen tawa.
repeating prep phrases vs using en (And I'm not sure if one is an error!)
suwi li tawa mi tawa sina. vs suwi li tawa mi en sina.
questions without seme
yes/no questions that dispense with the X ala X pattern
Conjoining sentences with taso, anu, en
Conjoining verb phrases with en instead of li. (less common)
Opatative/Hortative with o in wrong place
* mi mute o musi! Lets play! vs. o mi mute li musi!
* jan o utala ala! let there be peace vs o jan li utala ala!
Modifying prep phrase in the subject
soweli lon tomo mi li wile e moku. The cat in my house wants some food.