1. Yes, first time.
   

2. Same issue with SSMS, Data Studio and Synapse studio
   

3. Built in pool, created database (not master)
   

4. Cannot share, fairly complicated query. Basically a Fact view that joins to Dimension views to lookup surrogate keys. So something like:
   SELECT *
   FROM
   OPENROWSET (...)
   LEFT JOIN dbo.DimCustomer
   ON ...
   LEFT JOIN dbo.DimSector
   ON..

Would be easier if you could find out what the error message means?

The issue seems to have disappeared now. I would like to know if this is a bug or if there is something I can do if I recounter the issue?

No, same error from both Synapse studio and Azure Data Studio. One user reported the same issue around 2 weeks ago from SSMS (with SSMS generated Select top 1000 query). It is not a syntax error (at least on user side), I checked it in the query history as well. I also managed to restrict the issue to columns. By selecting only a subset of the columns in the external table the query would work. As mentioned in the post, the issue disappears after a while but it is concerning as it has happened more than once now and will confuse users.

Not sure, happens with every file I have:

Sorry, I haven't had time to look in to this earlier. I sent you a request ID that should have the issue. However, I cannot replicate the issue anymore. All queries that were previously having the issue are working properly now. Could it have been a temporary issue or something that got fixed?

Thank you for getting back to me. Good to hear that it is under development, then I will wait for the rollout.

Thank you for the update! Sounds promising, I will try it out!

Thanks for the reply, however it ignores information in the question. I have the Storage Blob Data Contributor assigned to both me and the managed identity. The private link does not work for the Serverless pool. What I mean is that On-Demand queries fail as soon as I uncheck the "Access to trusted Microsoft services..". The pipelines can still access the storage account so the private link works on that part but not the Serverless pool.

Strange indeed. However, it now works for me when I tried again today without any changes so the problem seemed to be related to synapse workspaces somehow.

I had this same problem in 2 different organizations. The groups exist, I could add the groups to a SQL Database and assign roles to the groups in the portal for various resources. I am also the Active Directory Admin for the Synapse workspace. I could add single users as users in the Synapse workspace, but adding the security group failed.

Thank you for your help, the problem seemed to solve itself.

Please see my answer below