Marketo-Facebook integration intermittently dropping

I am hoping someone can shed some light on an issue we have been having as Facebook, Marketo and Google are coming up short.

For years we have had a very successful Marketo-Facebook integration with thousands of leads coming through correctly. However every now and then, a handful of leads won't come through and are only picked up when we do a manual download of form leads and compare it against those already in Marketo. This drop in connection seems to happen over 2 days but as you can see from the screenshot, plenty of leads come in both before and after the drop as well as some leads coming in part way through the block.

So far I have:

Checked that the pages are still listed on launchpoint and confirmed the mappings are correct

Renewed the sync with launchpoint

Checked that Ad Bridge Prod is list and connected as a CRM on the page

Checked that the page has accepted Facebook terms and conditions
Confirmed that all relevant permissions are still granted

Does anyone have any ideas? We initially thought that we had reached our limit on API calls but don't think it could be this as the drop spans over 2 days and we still have some leads intermittently coming through during that time.

All help greatly appreciated