I've had a very strange complaint from a customer that has been setup on Office 365 quite soon and everything worked like in terms of their SharePoint Online for a few months. They're a very small company with less than 50 users. The scenario is the following:
- A couple of subsites under a root site collection in SharePoint Online
- A few document libraries underneath each site
- Some document libraries having 4-5 Managed Metadata columns in the default view
- Those same document libraries take about 30 seconds to load, compared to 1-3 seconds for the rest.
- None of the document libraries exceeds even a thousand documents.
- That issue appeared out of the blue, it was working fine for months.
I've done some tests to remove the Managed Metadata columns and prior to that, reviewed the term store to see if something is exceeding any limit or is in a contradiction with best practices.
After removing the Managed Metadata columns, the libraries started to load in 10x less time. That was very weird, as the columns have just a few choices, nothing that would potentially load the backend too much. Anyway I've decided to raise this with Microsoft and they resolved it in a few days. The first engineer just tried to replicate the issue on another Office365 test tenant, but he couldn't see such high load times. The escalation engineer, however solved it by working on the backend with their internal tools.
The explanation was the following:
"Using backend tools I was able to look up ECMPermissions table for the specified environment and delete any users that were not found in SPODS (user data base). After this action the issue was solved"
In plain English, that means that if you delete some users from an Office 365 tenant, sometimes there are orphaned records in this ECMPermissions table, and that has to be cleaned up manually. I haven't asked if they plan a hotfix or not, but after they intervened, the Managed Metadata is useful again.