@Sjaak01 ILM uses a poll interval of 10 minutes (indices.lifecycle.poll_interval) which defaults to 10 minutes.
The times in the phases are expected to be (considerably) larger than that, as @stephenb said. Your rollover with 1m and deletion with 5m is not helping that and could cause issues.
We don't recommend changing this value for production, but for a test you could set it to 1 minute.
Make your rollover be 2 or 3 minutes and your deletion 5 minutes.
Also your Logstash output is pointing to the ILM settings AND to the index name. So there might be a conflict, or simply the ILM settings are being ignored, making ingestion always happen in v2-testdiag-000001, not in the alias, which should change after rollover.
Remove the index name in the test. Logstash will create the index with the proper name and policy and actually write to the rollover alias, not to the first index as you specified.