Export list to Excel - a connection to the SharePoint list cannot be established

We are having an issue which appears to have just started (was working a few days ago) where exported lists in Excel, created using the List > Export to Excel command, cannot connect to the list to refresh when using Data > Refresh in Excel. This error (shown below) is returned in Excel just moments after exporting.

This happens when using Chrome, IE11 but only on this one site collection. This site collection is heavily used and did not have this problem prior to around a few days ago. Users tested have Full Control permissions on both site collections (I am site collection admin).

Switching to classic mode before exporting did not correct (I previously replied to another thread here but decided this is likely a different issue altogether so thought it best to start a new thread).

This is only affecting one site collection (the main one we use for data collection) but not any other site collections. I confirmed that Excel's connection properties appear to be appropriate in both cases so there must be something about this one particular site collection that is causing this although no changes were made to the settings or permissions of the affect site collection lately.

Does anyone know what site settings or other conditions might contribute to this not working anymore? Not really sure where to start looking.