Hi, and thanks for migrating your site to our server.
I investigated the issue on the copy of your site and found out that, indeed, it is a very similar issue as was reported with the Yoest SEO plugin here. https://wpml.org/errata/yoast-seo-stripping-category-base-not-working-when-the-taxonomy-slug-has-been-translated/
I'm sorry for missing this point earlier in our discussion. Luckily the temporary fix for this issue is the same as the workaround suggested on the errata page. What you need to do to fix this issue is this:
1. Go to WPML -> Taxonomy Translation and select 'Categories'.
2. Scroll down to the 'Translations of taxonomy Category labels and slug' section.
3. Edit the Spanish translation of the taxonomy.
4. Delete the value in the 'Slug' field and press the 'Save button. Please see the attached screenshot.
Now things should work properly.
Note: After doing this, you may need to sync the menu in WPML -> WP Menu Sync. This will fix the links in the Spanish menu.
I've escalated this issue to our compatibility team. When I have news regarding this issue, I'll update you here. Please let me know if you have further questions related to this issue.
This issue is escalated to our developers. We'll keep you updated here on any news regarding this issue. Meanwhile, please proceed with the suggested workaround. We also added an errata page on this issue which you can see here.