Angular ngx-translate strange behaviour

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Apache

Hi and thanks.

I've developed an angular app, implementing ngx-translate.
The translation works great on dev machine, and on 2 servers I've tested it on.
But... on one of the servers it doesn't work (I get the keys instead of translation values).

json files are available on the server (I can open them directly when accessing https://website/assets/i18n/??.json.

No error messages on the console.

Any ideas?

What I have tried:

Published on 3 different servers, with the same apache2 version.