Hi there,
We have just upgraded from 10.9.1 --> 11.1.
There is a builtin portal user account which has a large amount of content and owns a large number of groups ~163. What we are seeing is post upgrade when we try to share from an item we see this:

even though this user does own and belong to multiple groups.
When attempting to share I see a request to get the user back
https://someportal/arcgis/sharing/rest/community/users/someuser?f=json&token=atoken
which returns the user details and their groups - then there are 2 follow up requests
//someportal/arcgis/sharing/rest/community/groups?f=json&q=(isviewonly%3Afalse%20OR%200235a214dca848ffb1db46b3df43c1a8%20OR%200cf8f0139e3f4785bca2015b923631f2%20OR%201941d0b595624011b18a746e6f3bab64%20OR%201e45834c67264335bb318b404c7401cd%20OR%2024d81913f7c84783a421efd4e03ed211%20OR%20496c19eeb06e40c6b73c6c329c6aae90%20OR%204ee3fa9320e54c808e05f3b73401789a%20OR%206601aff4b2bd4ccdafb24e786be5a573%20OR%2079f2e1d7018d4cf8a2448c72933dcc68%20OR%207d51672c405c47f2bc2639dd33bbd52f%20OR%207da67743d70948fcaef09d70c72aaf48%20OR%20806e54dc89694e9a9747fc37634dfa21%20OR%20824f7ee897034d68b5fe55c308f64cd8%20OR%2082b8bf57a3cd455f94ee6ac6a5caa45a%20OR%20888f2e6a53ab4c45afa33a1e2d9c0703%20OR%209db4dff2c9614023b7a122de5ddf3f13%20OR%209f37e19c926448de823607df2c94e87c%20OR%20a3468dfb497c4983b7a33c2d8517f680%20OR%20a85c75a39ebf4fcf9e227bf13ebc2785%20OR%20ac42d9cb72574da89111899f90544c47%20OR%20acf42ba560014311ad7ddff88f6b23ee%20OR%20b60bc72331ed4848aad1073a56b209e3%20OR%20b6f5b7cf4c9e42b0922e531ad090dba1%20OR%20b7d32629a08244ceb5640b0d032c9bd3%20OR%20bc05396c45ca4475a1d9d36936e47a96%20OR%20bea88b16ee234f1384b2358f9cc0a4eb%20OR%20c14503b3fc664d22b5938a270d7fc747%20OR%20d6e17013375d4e9aa49ee21cf3c8acf7%20OR%20d7c3e093cb9d410daa83cf487e14366a%20OR%20da54c17247444483bc2c32105a274636%20OR%20dd165b4388024970ab7013c17da8f2b8%20OR%20e51ca3e60c3e4540805ff0216c54a0d3%20OR%20eeccca78191c41cda09dd1e7bc2fd39e%20OR%20f1a3680d317046d3a7b58d9f77c7b145%20OR%20f42c32153c70478aa2625973ea3016d8)&num=100&sortField=title&sortOrder=asc&start=1&searchUserAccess=groupMember&searchUserName=someuser&token=sometoken
this returns
{"total":0,"start":0,"num":0,"nextStart":0,"results":[]}
and it duplicates
//someportal/arcgis/sharing/rest/community/groups?f=json&q=(isviewonly%3Afalse%20OR%200235a214dca848ffb1db46b3df43c1a8%20OR%200cf8f0139e3f4785bca2015b923631f2%20OR%201941d0b595624011b18a746e6f3bab64%20OR%201e45834c67264335bb318b404c7401cd%20OR%2024d81913f7c84783a421efd4e03ed211%20OR%20496c19eeb06e40c6b73c6c329c6aae90%20OR%204ee3fa9320e54c808e05f3b73401789a%20OR%206601aff4b2bd4ccdafb24e786be5a573%20OR%2079f2e1d7018d4cf8a2448c72933dcc68%20OR%207d51672c405c47f2bc2639dd33bbd52f%20OR%207da67743d70948fcaef09d70c72aaf48%20OR%20806e54dc89694e9a9747fc37634dfa21%20OR%20824f7ee897034d68b5fe55c308f64cd8%20OR%2082b8bf57a3cd455f94ee6ac6a5caa45a%20OR%20888f2e6a53ab4c45afa33a1e2d9c0703%20OR%209db4dff2c9614023b7a122de5ddf3f13%20OR%209f37e19c926448de823607df2c94e87c%20OR%20a3468dfb497c4983b7a33c2d8517f680%20OR%20a85c75a39ebf4fcf9e227bf13ebc2785%20OR%20ac42d9cb72574da89111899f90544c47%20OR%20acf42ba560014311ad7ddff88f6b23ee%20OR%20b60bc72331ed4848aad1073a56b209e3%20OR%20b6f5b7cf4c9e42b0922e531ad090dba1%20OR%20b7d32629a08244ceb5640b0d032c9bd3%20OR%20bc05396c45ca4475a1d9d36936e47a96%20OR%20bea88b16ee234f1384b2358f9cc0a4eb%20OR%20c14503b3fc664d22b5938a270d7fc747%20OR%20d6e17013375d4e9aa49ee21cf3c8acf7%20OR%20d7c3e093cb9d410daa83cf487e14366a%20OR%20da54c17247444483bc2c32105a274636%20OR%20dd165b4388024970ab7013c17da8f2b8%20OR%20e51ca3e60c3e4540805ff0216c54a0d3%20OR%20eeccca78191c41cda09dd1e7bc2fd39e%20OR%20f1a3680d317046d3a7b58d9f77c7b145%20OR%20f42c32153c70478aa2625973ea3016d8)&num=100&searchUserAccess=groupMember&searchUserName=someuser&token=sometoken
with
{"total":0,"start":0,"num":0,"nextStart":0,"results":[]}
It seems to be the number of group ids in the query with the ORs - if you drop it down (change the query say from postman then it works as expected (remove a bunch of the OR id OR id etc).
The other thing I saw is if you move some of the existing groups to another owner then the item sharing works - if you move them back it stops working - this was at around 60 groups. This only seems to be with existing groups / users - as I created a new user and 300 test groups that they owned and sharing worked as expected.
I'm wondering if the sharing API is throwing an internal exception and just returning a default response rather than the error. I'm digging into the tomcat logs to see if anything is in there but I suspect the exception if there is one has already been swallowed.
Nothing in portal logs.
Has anyone come across this before?
Thanks
Fraser