Ibland missar bussen mig!
why can't I use "saknar" in stead of "missar" (both are given in the hints)
sakna means to miss as in "I miss him terribly".
How do we know that the sentence doesn't relate to a feeling? Surely 'I always catch the bus' should have been used for clarity. Duo does this a lot and if it's difficult to ascertain intent in my own language then what hope do I have in another?!
If a lack of context makes a sentence too ambiguous, both options are accepted. But in the case of missing a bus, I don't really think context is required to pick the sensible option.
Would it be totally wrong to put aldrig at the end, just a little odd, or perfectly fine?
No, it sounds weird to me.
Can one nor place aldrig before missar?
No, because the verb must be in second place in the sentence (the V2 rule).
Aldrig missar jag bussen? Is that okay or does it soubd weird?
It's grammatical but very unidiomatic. You'll likely never encounter it outside of e.g. poetry and lyrics.