Difficulty learning fractions is because:
Fractions today are taught at times in ways similar to the concept in Euclid of a proportion. This approach’s logic is hard to follow as we try to place more of the requirements of number on fractions.
Eventually, the Euclid way was abandoned and 19th century mathematicians started over with object oriented ordered pairs of data and procedures specifically defined to make fractions have the desired properties. This is the modern concept of fraction. However, schools still teach the unworkable pre-modern approach to fractions. This eventually runs into the same problems all over again for each new generation of students.
The education establishment refuses to switch the same way the mathematicians did, so they are left on their own spinning endlessly with an approach that lacks the simplicity and coherence of ordered pairs. Students can’t learn it because it doesn’t actually make sense to them in the midst of all the sound and noise.
Schools keep asking for more money, more student time in school, and more homework time in pushing a failed concept on each new cohort of students. This just fails bigger and bigger each time. Only an intervention can succeed in changing this.