Hi.
I noticed that k2 feeds don't update when i add new articles.
It seems like the feed listitem is generated once on a first visit and then no new items get added.
However, when i introduce changes to articles, the feed changes as well. Just no new feeds appear after first visit.
Obviously, i excluded cache issues from the culprit list.

I reproduced this error on two different installations of Joomla with K2 component.
I also checked the feed for regular categories/articles - they appear in rss feed no problem after being added.
new k2 articles appear ok in the frontend, only when i add ?format=feed&type=rss to the URL i cant get the correct feed from category.

site in question:
4tour.pl/szczawnica/wydarzenia-regionalne-szczawnica
with a sample feed
4tour.pl/szczawnica/wydarzenia-regionalne-szczawnica?format=feed&type=rss

Im running out of ideas here.

Hello,

What are your caching settings Jerzy?

disabled in global-> system settings
module -> no caching as well

I just tried to reproduce the problem on a fresh installation.
I created a simple k2 category and added some items - so good so far: the feeds get updated.
Then I decided to go further and imported the following tables from problem site: #__k2 items, #__k2_categories, #__k2_extra_fields, #__k2_extra_fields_groups.
Yup. the feed problem has been reproduced.
I would attach sql dumps but the 'add file' button doesn't seem to respond.

Which other K2 related extensions are you using?

fresh install. only k2

I mean the site that has the issue.

k2 tools
k2 users
k2 user
k2 comments
k2 filter & search module

all enabled

Can you deactivate the k2 filter & search module and see if the issue is resolved?
In the link you sent me - 4tour.pl/szczawnica/wydarzenia-regionalne-szczawnica - the very first item is REDYK – Tradycyjny przepęd owiec po okolicznych halach
In the feed this is the item displayed as well, this means that the output is correct.
Have you tried adding a new item?

PS, Since the actual output is being generated by Joomla!, the feeds will not abide to the filtering options (which use CSS to only hide/show items), the first items (in relation to the DOM) will always be shown.

unfortunately, no changes.