Short Grammar Questions (Part 1)

Not really grammar, but I’ve been mulling over it for some time now.
I generally get the reason why one word should be in kanji or in kana. When to Use Kanji vs Kana
But why are some words (verbs?) split? The first part in kanji, the second in kana?

For example this sentence:

かの女は失れんしてとても悲しんでいます。 (WK vocabulary 悲しむ)
She got dumped and she’s very sad.

Why is the second part of 失れんして (or better 失れん) in kana?
I would have used 失恋して .

Considering it’s a WK word it’s confusing. It’s a word from the same level (lv 17) so one would see it in a couple of days anyway. I’ve seen the same thing in other Context Sentences, often with kanji we should already know or have just learned.

Is it a didactical choice the WK team made? Is it just the more common version in Japanese? Is it common to split words or verbs (using kanji only at the beginning) in Japanese?

Thanks in advance to anyone willing to explain