These tickets usually come in as forwarded emails from Google similar to the following:
Robots.txt
The robots.txt file is the same for every one of our sites and pages that are blocked are intentional, usually to avoid duplicate content penalties on listing results and to block from crawling the search results since they are dynamic and not indexable. Having the same content appear on various webpages can lead to SEO rankings being hurt for being flagged as duplicate content. This is something that Google does to prevent content from being stolen. Here is Google's article about it for a little more information: Introduction to robots.txt
'noindex' tag
Property detail pages aren't indexed by default because they run the risk of being counted as 'duplicate content', since they're built from the IDX data and thus any other site on the same feed is going to have similar or identical prop detail pages. You can turn on indexing for them though by going to Website Settings in the backend, then to Advanced Site Settings > Index Detailed Properties. But if Google flags it as duplicate content it would be a negative hit to the SEO.
"Crawled - currently not indexed"
Google will crawl the site and some pages are indexed (or "cleared") right away and some take time. This happens most frequently with new sites the first go and this section will decrease over time. From one of our dev team: The total time can be anywhere from a day or two to a few weeks, typically, depending on many factors.
"404 and 4xx errors"
This will actually occur when anyone accesses specific logged in pages of the site (saved searches, etc). Google notices that there is activity on the site but cannot access the pages because it is logged in as a user. This should not affect the indexing of the proper pages of the site.
"Duplicate without user-selected canonical"
These "indexing issues" emails are always a bit jarring, but this is not an issue that will actually affect your site's search performance or ranking.
From Google's support page on this indexing "error" Google - Page Indexing report
This page is a duplicate of another page, although it doesn't indicate a preferred canonical page. Google has chosen the other page as the canonical for this page, and so will not serve this page in Search. You can Inspect this URL to see which URL Google considers canonical for this page.
This is not an error, but is working as intended, because Google does not serve duplicate pages. However, if you think that Google has chosen the wrong URL as canonical, you can explicitly mark the canonical for this page. Alternately, if you think that this page is not a duplicate of the Google-chosen canonical, you should ensure that the content differs substantially between the two pages.