We have a webshop for the six countries Belgium, Netherlands, Luxembourg, Italy, France and Denmark. We have a total of 15 language versions for the six countries. For example, the pages in Belgium exist in French, Dutch, German and English. The different language versions are sorted in different folders like "fr-be", "nl-be", "de-be" or "en-be". We have linked all language versions of a page with hreflang tags and all pages have a canonical tag.
E.g.
<link rel="canonical" href="https://www.example.com/en-be">
<link rel="alternate" href="https://www.example.com/fr-be" hreflang="fr-be" >
<link rel="alternate" href="https://www.example.com/nl-be" hreflang="nl-be" >
<link rel="alternate" href="https://www.example.com/de-be" hreflang="de-be" >
<link rel="alternate" href="https://www.example.com/en-be" hreflang="en-be" >
<link rel="alternate" href="https://www.example.com/nl-nl" hreflang="nl-nl" >
<link rel="alternate" href="https://www.example.com/en-nl" hreflang="en-nl" >
<link rel="alternate" href="https://www.example.com/fr-lu" hreflang="fr-lu" >
<link rel="alternate" href="https://www.example.com/de-lu" hreflang="de-lu" >
<link rel="alternate" href="https://www.example.com/en-lu" hreflang="en-lu" >
<link rel="alternate" href="https://www.example.com/fr-fr" hreflang="fr-fr" >
<link rel="alternate" href="https://www.example.com/en-fr" hreflang="en-fr" >
<link rel="alternate" href="https://www.example.com/it-it" hreflang="it-it" >
<link rel="alternate" href="https://www.example.com/en-it" hreflang="en-it" >
<link rel="alternate" href="https://www.example.com/da-dk" hreflang="da-dk" >
<link rel="alternate" href="https://www.example.com/en-dk" hreflang="en-dk" >
<link rel="alternate" href="https://www.example.com" hreflang="x-default" >
However, we have massive indexing problems. More than one year after launchning the shop, still many important pages (linked in the menu) are not indexed. Especially, we have the problem that usually only one version of the respective language is indexed by Google. For example, there are three French versions. In the Search Console, however, we can see that only one of the three versions is indexed and the other two versions are considered duplicates.
We don't have a ton of backlinks but at least some high quality links pointing to the shop. Moreover, we have redirected (301) our old shops for France, Denmark and Italy to the new one. Even pages which are correctly redirected are not indexed.
Anyhow, the indexiering problems are still there. Especially the fact that Google seems to ignore canonical and hreflang and treat pages as duplicates is annoying. Also, the number of indexed pages is decreasing the last weeks.
Any ideas, what else can we do?