For troubleshooting, trail data can be accessed using the Oracle GoldenGate LogDump Utility Commands. Your will be able to identify long transactions, determine data at a particular RBA position, etc..
The Goldengate HANDLECOLLISIONS parameter is configured on the Replicat side to continue processing of the data when there are data integrity issues on the destination side and is okay to do so. It is utilized when there is a possibility of an overlap of the trail data being applied by the replicat process (replicat) where the data already exists in the destination tables.
For replication to be robust, well tuned and secure, some out of the box settings need to modified. Here is a list of these items, focusing on the Goldengate Best Practices and Security, in areas such as the Database, Parameters, processes, etc. Read more here.