We are in the process of upgrading several EE cms instances from v2.8.1 to v3.5.7 and have run into an issue. Each instance is running 2.8.1 with the MSM and 50 sites enabled (though in some cases not all used).
After successfully running the upgrade, we cannot view any of the existing channel entries through the Control Panel. We have confirmed that all entries are present in the exp_channel_titles and exp_channel_entries database tables. Also the Control Panel homepage boxes list correctly the Channels, Members and Content relevant to a given site. However, clicking Edit > View All or Edit > Channel results in an Entry Manager page with "No entries found"
If we publish an entry to any given channel it will save to both database tables as expected but is not viewable through the Control Panel.
Does anyone know why this might be and how to fix it?