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I know you're not going to be happy with this, but I'm going to write up an answer in English. First, at least.
First about digitization:
Amazon has the same problem you do. They don't know how to render the character. I haven't looked into it very deeply but it looks like they have issues with CJKV extensions. (Perhaps CJK Ext. A is more doable, but I'm not sure about B-G.)
𪨊 (⿸尸从) is a CJK Ext. C character.
CJK Ext. characters usually need special font support and that clearly hasn't been implemented into Amazon or Kindle products.
𪨊 can be found in Mandarin dictionaries:
weak and incompetent
weak by nature
weak and incompetent
Perhaps the most well known word with this character is: 𪨊包.
For the sake of understanding you can consider 秒𪨊 two "words," instead of one single word.
"秒 + verb" has become a trend in neologisms. There are quite a few of these combinations, think: 秒懂，秒回，秒赞，秒睡，秒删, etc. 秒𪨊 is a combination of "instant" + "cower."
秒怂：become chicken immediately
秒: Second, here means within a second, or immediately.
Its most original usage is in the word 秒杀, killed immediately. This is a word used in gaming so kill means pass a game stage or win a battle game. So later on 秒杀 means "solved immediately". For example, A: how was your exam? B: 秒杀。
Also see 秒懂 understand immediately, 秒过 pass (interview) immediately.
怂 (adj) ,chicken, cowardly.
怂是一个汉字，读音为sǒng，基本释义：1.〔～恿〕鼓动别人去做某事；2.惊，惊惧。 网络用语中，该字又被用作“㞞”（sóng ）的讹借字，义“讽刺人软弱无能”。
Based on the explanation, 㞞 is the correct character. And 從 is 从, so the paper copy is correct. Most people just don't know it and substitute by 怂 which have a similar pronunciation.
This character is mostly a dialect, and then used a lot on web. I heard this word in conversations maybe after 2013 or 14, and never really read or write it at that time. I bet most people are the same as me. When typing it, just type "song" and use the most plausible one, mostly because of the 心 part. Interestingly, the Google pinyin input method even does not have the character 㞞.
Here in the fiction, I guess it mean he became chicken immediately and not brave anymore.