Website Indexing Fixing of 5 year lod news wordpress website

RHN.ro is the website. There are a few static pages to which a database of ~17800 articles of news (17600 in the main language Romanian and 200 in a translation language English done with the plugin of WPML). For 5 years i have been using XML Sitemap Generator for Google as i had indexing issues. From time to time i get indexing emails from Google saying that there are huge problems, i ignored them but a few days ago i decided to look into it and i found :
- there are 98k not-indexed links and 27.6k indexed links (how is this possible if i only have the above mentioned number of articles and a few campaigns generating some more pages for each campaing i am sending using Mailster plugin)

The largest number of problems are from:
Crawled - currently not indexed 59900
Alternate page with proper canonical tag 15900
Not found (404) 9800
Discovered - currently not indexed 8300
Page with redirect 1800
Excluded by ‘noindex’ tag 800
Server error (5xx) 700
Blocked due to access forbidden (403) 400
Duplicate without user-selected canonical 269
Soft 404 40
Duplicate, Google chose different canonical than user 6
Blocked due to other 4xx issue 1

I need somebody to fix these problems once and for good...look at my plugins, my server is at the moment also reacting very slow ...