WordPress API error: Failed to insert new item. WP API returned no valid post ID

Hello,
what do these errors mean? FeedWordpress doesn’t create the posts from these 2 feeds but the validator says that they are valid.

Item [http://.......wordpress.com/?p=2340] "Post title" is a NEW POST.
Inserting new post "Post title"
WordPress API error: Failed to insert new item [http://.......wordpress.com/?p=2340]. WordPress API returned no valid post ID.
ID = O:8:"WP_Error":2:{s:6:"errors";a:1:{s:15:"db_insert_error";a:1:{i:0;s:44:"Impossibile inserire l'articolo nel database";}}s:10:"error_data";a:0:{}}
URL = string(72) "https://........wordpress.com/2020/02/10/post-title/"
Feed = string(43) "http://........wordpress.com/feed"

Item [tag:blogger.com,1999:blog-xxxxxxxx.post-xxxxxxxx] "Post title" is a NEW POST.
Inserting new post "Post title"
WordPress API error: Failed to insert new item [tag:blogger.com,1999:blog-xxxxxxxx.post-xxxxxxxx]. WordPress API returned no valid post ID.
ID = O:8:"WP_Error":2:{s:6:"errors";a:1:{s:15:"db_insert_error";a:1:{i:0;s:44:"Impossibile inserire l'articolo nel database";}}s:10:"error_data";a:0:{}}
URL = string(82) "http://........blogspot.com/2019/10/post-title.html"
Feed = string(56) "http://........blogspot.com/feeds/posts/default"

I’m using Feedwordpress 2016.0420 on WordPress 4.4.21 (I know it’s not the latest version but I can’t update WordPress right now).