Hi marion33678522,
The best way to test this is by QA'ing your app. Most likely there is a call being made to the collection servers that does not have any values sent that define the Custom Link. Here's my suggestion:
1 - use Workspace in order to try to narrow down "when/where" the custom link is called. One idea is to use Flow reporting. Use Custom Link as the dimension being analyzed in the Flow component and find the unpleasant "AMACTION:". Click to see what the previous Custom Link was. Or, switch the previous column to Page to see what screen the Custom Link is getting called from.
2 - use Bloodhound (or Charles Proxy) to QA your app. Here's a primer on Using Bloodhound to Test Mobile Applications and try to replicate the flow that you discovered to find the Custom Link culprit(s).
Hope that helps!