Help Tracing an API Call from uclient/scripts

app.js?v=1.4.2799-2106.3:2672 [storage] Error Messages: 
1: *** With Id = *** Does Not Exist
    at K (https:// (***.crm.dynamics.com/uclient/scripts/app.js?v=1.4.2799-2106.3:2675:407)
    at new u (https://***.crm.dynamics.com/uclient/scripts/app.js?v=1.4.2799-2106.3:1897:1299)
    at https://***.crm.dynamics.com/uclient/scripts/61.js?v=1.4.2799-2106.3:20:18771
    at https://***.crm.dynamics.com/uclient/scripts/61.js?v=1.4.2799-2106.3:20:19426
Call stack hash: 0

My team has spent a few days trying to trace this error, and now I'm asking for your help.

We've checked all our web resources and disabled all event handlers, but all to no avail.

If you were on my team, where would you look?

Thank you,

David