I have a similar problem (not related to vue.js and amazon, but just to Subject: Safari selectively loads resources):
Mac OS Safari 14 (desktop version, I don't know for a mobile one) doesn't load all referred css, js, and image files.
Safari 13 performed well. Other browsers (Chrome, Firefox) perform well. All files are referred the same way, using relative URLs.
When using Safari 14, some of them are loaded, some are not. Caching is not an issue (I use "empty caches" before loading a page).
It looks like successfully loaded files are randomly chosen (the same file is sometimes loaded, sometimes it isn't).
In the Network tab of Develop menu, for not loaded files Preview says: "An error occurred trying to load the resource",
and in Headers, section "Request", there are only: Accept, Referer, and User-Agent lines, while:
GET, Cookie, Accept-Encoding, Host, Accept-Language, and Connection lines are missing.
Response says: "No response headers".
In the server's access log, there are no lines related to not loaded files.
EDIT:
The cause: TLS 1.0
The solution: TLS 1.2
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