Bug Very weird bug related to unity's serialization(?)

I've been using unity's localization for a while and the project has quite a lot of keys in the tables by now. I think I've hit a really weird edge case which broke unity's serialization. While working on my game I started getting weird errors:
"Unable to parse file X [Parser Failure at line Y: Expect ':' between key and value within mapping]"
where X is a string table asset.
Tried restarting the project, reimporting the assets. Nothing helped.

I checked the line number mentioned in the error and I found this in the asset file:

m_Localized: "\u6539\u9020\u30A2\u30A4\u30C6\u30E0\u304C\u3042\u308A\u307E\u305B\u3093\nID:
{0}\n\u30E2\u30C3\u30C9\u540D: {1}\nMod guid: {2}"

It's really weird as it appears as if the ":" in the localized text somehow breaks the parser. In the end I fixed it by clearing the m_Localized value in the asset and using a slightly different text for this entry.

Out of curiosity I tried creating a new entry in the string table with the following text.
改造アイテムがありません
ID: {0}
モッド名: {1}
Mod guid: {2}

And the error appeared again. Very weird. I'm using Unity 2020.3.38f1 with localization package 1.4.3

 

I will try to reproduce it on a minimal project and file a bug report if I find some time. Very busy working on a new update of my game now though, so probably not very soon.