Exception when in multi-project setup

[Former user]

for projects with multiple sub-projects I always get following exception:

Caused by: java.util.ConcurrentModificationException
    at org.gradle.api.internal.collections.FilteredCollection$FilteringIterator.findNext(FilteredCollection.java:121)
    at org.gradle.api.internal.collections.FilteredCollection$FilteringIterator.next(FilteredCollection.java:140)
    at org.gradle.api.internal.collections.FilteredCollection$FilteringIterator.findNext(FilteredCollection.java:121)
    at org.gradle.api.internal.collections.FilteredCollection$FilteringIterator.next(FilteredCollection.java:140)
    at org.gradle.api.internal.DefaultDomainObjectCollection$IteratorImpl.next(DefaultDomainObjectCollection.java:479)
    at com.patdouble.gradle.awsecr.AwsecrPlugin.configureRegistryCredentials(AwsecrPlugin.groovy:113)