Mixed branches / targeting countries results in the SERP

[execom99]

hi all, I have one hard nut to break and I would like to kindly ask you for any idea / help
we have web page localized to multiple languages targetting different countries.
e.g. we have:

domain.com/int/ ... default in english, in search console / Internation targeting / Country with Target users in "Unlisted"
domain.com/uk/ ... english for UK, Target users in "United Kingdom"
domain.com/de/ ... german content for Germany, Target users in "Germany"
... etc.

Each branch (country specific) has its own sitemap.xml covering approx 50-60% of all the pages for the specific branch and for most of these pages we have set hreflang (rel="alternate") for most important product pages. There are some issues in the sitemaps we are fixing (e.g. no returning link) so my assumption is that google may not use the sitemap, therefore, hreflang is not in use (it is part of sitemap). For example, one branch can have 150 pages submitted and 30 indexed in Sitemap detail of search console.

The problem is, that when for example I search for the product name from Germany (google.de and German's IP through VPN in browser's incognito mode) I'm receiving mixed results. Our product names and technology are rather english, e.g. "cloud protection" and it is also phrase German user would search for. But in SERP he gets results from our domain.com/uk and also from our domain.com/sg which is completely wrong.

Is there a way to really prevent it ?
thanks
T