Have you set the field to translate in WPML > Translation settings?
There are listed all Custom Types and Fields, and you should have selected translate there as well.
It is important that both Types and WPML register it as fully translatable and does not copy or sync elsehow the posts/fields
Well - I checked with fresh install, even you can check here:
=> hidden link
Once you are at wp-admin, I created test posts and translated it as well:
=> hidden link
I've added one image field and one file field (which is set to "Translate") and I can see it just works fine. Could you please confirm it works at your end as well as well as let me know if I miss any step here?
I'm testing but the whole page does not work, I'm referring to the page: hidden link
Anything I change is not taken. I checked and the field translation settings are correct, I have performed the "copy from the original" not the "overwrite from the original". If it can help: there are no mandatory fields, there are more conditional fields.